Driving device, air conditioner, and method for driving motor

ABSTRACT

A driving device drives a motor having coils. The driving device includes a converter to generate a bus voltage, an inverter to convert the bus voltage to an AC voltage and supply the AC voltage to the coils, and a connection switching unit to switch a connection state of the coils. The bus voltage generated by the converter is switched in accordance with the connection state of the coils.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of InternationalPatent Application No. PCT/JP2016/082208 filed on Oct. 31, 2016, thedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a driving device for driving a motor,an air conditioner including the motor, and a method for driving themotor.

BACKGROUND

In a motor for use in an air conditioner and the like, a connectionstate of coils of the motor is switched between a Y connection (starconnection) and a delta connection (also referred to as a Δ connection)in order to enhance operation efficiency during low-speed rotation andduring high-speed rotation (see, for example, Patent Reference 1).

Specifically, control is performed in such a manner that a rotationspeed of the motor is compared to a threshold, and switching from the Yconnection to the delta connection is performed when a state in whichthe rotation speed is higher than or lower than a threshold continuesfor a certain time period (see, for example, Patent Reference 2).

PATENT REFERENCE

-   -   Patent Reference 1: Japanese Patent Application Publication No.        2009-216324    -   Patent Reference 2: Japanese Patent Publication No. 4619826

In this case, however, it is difficult to sufficiently enhanceefficiency of the motor simply by switching between the Y connection andthe delta connection.

SUMMARY

The present invention is made to solve the problem described above, andan object of the present invention is to sufficiently enhance efficiencyof a motor.

A driving device according to the present invention is a driving deviceto drive a motor having coils, and includes a converter to generate abus voltage, an inverter to convert the bus voltage to an AC voltage andsupply the AC voltage to the coils, and a connection switching unit toswitch a connection state of the coils. The bus voltage generated by theconverter is switched in accordance with the connection state of thecoils.

According to the present invention, the bus voltage of the converter isswitched in accordance with the connection state of the coils, and thusmotor efficiency can be sufficiently enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a configuration of a motoraccording to a first embodiment.

FIG. 2 is a cross-sectional view illustrating a configuration of arotary compressor according to the first embodiment.

FIG. 3 is a block diagram illustrating a configuration of an airconditioner according to the first embodiment.

FIG. 4 is a conceptual diagram illustrating a basic configuration of acontrol system of the air conditioner according to the first embodiment.

FIG. 5(A) is a block diagram illustrating the control system of the airconditioner according to the first embodiment, and FIG. 5(B) is a blockdiagram illustrating a section that controls the motor of the compressorbased on a room temperature.

FIG. 6 is a block diagram illustrating a configuration of a drivingdevice according to the first embodiment.

FIG. 7 is a block diagram illustrating a configuration of the drivingdevice according to the first embodiment.

FIGS. 8(A) and 8(B) are schematic diagrams illustrating a switchingoperation of a connection state of coils according to the firstembodiment.

FIG. 9 is a schematic diagram illustrating the connection state of thecoils according to the first embodiment.

FIG. 10 is a flowchart showing a basic operation of the air conditioneraccording to the first embodiment.

FIG. 11 is a flowchart showing a connection switching operation of theair conditioner according to the first embodiment.

FIG. 12 is a flowchart showing a connection switching operation of theair conditioner according to the first embodiment.

FIGS. 13(A) and 13(B) are flowcharts showing other examples of theconnection switching operation of the air conditioner according to thefirst embodiment.

FIG. 14 is a timing chart showing an example of an operation of the airconditioner according to the first embodiment.

FIG. 15 is a graph showing a relationship between a line voltage and arotation speed of the motor in a case where coils are connected in a Yconnection.

FIG. 16 is a graph showing a relationship between the line voltage andthe rotation speed of the motor in a case where the coils are connectedin the Y connection and field-weakening control is performed.

FIG. 17 is a graph showing a relationship between motor efficiency and arotation speed in a case where the field-weakening control shown in FIG.16 is performed.

FIG. 18 is a graph showing a relationship between motor torque and therotation speed in a case where the field-weakening control shown in FIG.16 is performed.

FIG. 19 is a graph showing relationships between the line voltage andthe rotation speed in the case where the connection state of the coilsis a Y connection and in the case where the connection state of thecoils is a delta connection.

FIG. 20 is a graph showing a relationship between the line voltage andthe rotation speed in a case where switching from the Y connection tothe delta connection is performed.

FIG. 21 is a graph showing relationships between the motor efficiencyand the rotation speed in the case where the connection state of thecoils is the Y connection and in the case where the connection state ofthe coils is the delta connection.

FIG. 22 is a graph showing a relationship between the motor efficiencyand the rotation speed in a case where the connection state of the coilsis the Y connection, the number of turns is adjusted such that the linevoltage reaches an inverter maximum output voltage at a rotation speedslightly lower than that in an intermediate heating condition, andswitching from the Y connection to the delta connection is performed.

FIG. 23 is a graph showing relationships between the motor torque andthe rotation speed in the case where the connection state of coils isthe Y connection and in the case where the connection state of coils isthe delta connection.

FIG. 24 is a graph showing a relationship between the motor torque andthe rotation speed in the case where the connection state of the coilsis the Y connection, the number of turns is adjusted such that the linevoltage reaches the inverter maximum output voltage at the rotationspeed slightly lower than that in the intermediate heating condition,and switching from the Y connection to the delta connection isperformed.

FIG. 25 is a graph showing a relationship between the line voltage andthe rotation speed in a case where a bus voltage is switched by aconverter.

FIG. 26 is a graph showing a relationship between the line voltage andthe rotation speed in a case where switching of the connection state ofthe coils and switching of the bus voltage of the converter areperformed in the first embodiment.

FIG. 27 is a graph showing relationships between the motor efficiencyand the rotation speed in the case where the connection state of thecoils is the Y connection and in the case where the connection state ofthe coils is the delta connection.

FIG. 28 is a graph showing a relationship between the motor efficiencyand the rotation speed in a case where switching of the connection stateof the coils and switching of the bus voltage of the converter areperformed in the first embodiment.

FIG. 29 is a graph showing relationships between the motor torque andthe rotation speed in the case where the connection state of the coilsis the Y connection and in the case where the connection state of thecoils is the delta connection.

FIG. 30 is a graph showing a relationship between the motor efficiencyand the rotation speed in the case where switching of the connectionstate of the coils and switching of the bus voltage of the converter areperformed in the first embodiment.

FIGS. 31(A) and 31(B) are graphs each showing a relationship betweenmotor efficiency and a rotation speed in a first modification of thefirst embodiment.

FIG. 32 is a graph showing a relationship between a line voltage and arotation speed in a second modification of the first embodiment.

FIGS. 33(A) and 33(B) are schematic diagrams for describing a switchingoperation of the connection state of the coils in a third modificationof the first embodiment.

FIGS. 34(A) and 34(B) are schematic diagrams for describing anotherexample of the switching operation of the connection state of the coilsin the third modification of the first embodiment.

FIG. 35 is a flowchart showing a connection switching operation in afourth modification of the first embodiment.

FIG. 36 is a flowchart showing a connection switching operation in afifth modification of the first embodiment.

FIG. 37 is a block diagram illustrating a configuration of an airconditioner according to a second embodiment.

FIG. 38 is a block diagram illustrating a control system of the airconditioner according to the second embodiment.

FIG. 39 is a block diagram illustrating a control system of a drivingdevice according to the second embodiment.

FIG. 40 is a flowchart showing a basic operation of the air conditioneraccording to the second embodiment.

FIG. 41 is a flowchart showing a basic operation of an air conditioneraccording to a modification of the second embodiment.

DETAILED DESCRIPTION First Embodiment

(Configuration of Motor)

A first embodiment of the present invention will be described. FIG. 1 isa cross-sectional view illustrating a configuration of a motor 1according to the first embodiment of the present invention. The motor 1is a permanent magnet embedded type motor, and is used for a rotarycompressor, for example. The motor 1 includes a stator 10 and a rotor 20rotatably provided inside the stator 10. An air gap of, for example, 0.3mm to 1 mm is formed between the stator 10 and the rotor 20. FIG. 1 is across-sectional view taken along a plane perpendicular to a rotationaxis of the rotor 20.

Hereinafter, an axial direction (direction of the rotation axis) of therotor 20 will be simply referred to as an “axial direction”. A directionalong an outer periphery (circumference) of each of the stator 10 andthe rotor 20 will be simply referred to as a “circumferentialdirection”. A radial direction of each of the stator 10 and the rotor 20will be simply referred to as a “radial direction”.

The stator 10 includes a stator core 11 and coils 3 wound around thestator core 11. The stator core 11 is made by stacking a plurality ofelectromagnetic steel sheets each having a thickness of 0.1 mm to 0.7 mm(0.35 mm in this example) in the direction of the rotation axis andfastening the sheets by crimping.

The stator core 11 includes a ring-shaped yoke 13 and a plurality of(nine in this example) tooth portions 12 extending inward in the radialdirection from the yoke 13. A slot is formed between adjacent ones ofthe tooth portions 12. Each of the tooth portions 12 has a tooth endpart at an end on an inner side in the radial direction, and the toothend part has a wide width (dimension in the circumferential direction ofthe stator core 11).

The coil 3 as a stator winding is wound around each of the toothportions 12 via an insulator 14. The coil 3 is obtained by, for example,winding a magnet wire having a wire diameter (diameter) of 0.8 mm aroundeach of the tooth portions 12 by concentrated winding in 110 turns. Thenumber of turns and the wire diameter of each coil 3 are determinedbased on characteristics (rotation speed, torque or the like) requiredfor the motor 1, a supply voltage, or a cross-sectional area of theslot.

The coils 3 are constituted by three-phase windings of a U-phase, aV-phase, and a W-phase (hereinafter referred to as coils 3U, 3V, and3W). Both terminals of the coil 3 in each phase are open. That is, thecoils 3 have six terminals in total. A connection state of the coils 3is switchable between a Y connection and a delta connection, which willbe described later. The insulator 14 is made of, for example, a film ofpolyethylene terephthalate (PET), and has a thickness of 0.1 mm to 0.2mm.

The stator core 11 has a configuration in which a plurality of (nine inthis example) blocks are coupled to each other via thin portions. Themagnet wire is wound around each of the tooth portions 12 in a statewhere the stator core 11 is extended in a band shape, and then thestator core 11 is bent into a ring shape and both ends of the statorcore 11 are welded.

A configuration in which the insulator 14 is made of a thin film and thestator core 11 has a divided structure in order to facilitate winding asabove is effective for increasing the number of turns of the coil 3 inthe slot. In this regard, the stator core 11 is not limited to the abovedescribed configuration in which the plurality of blocks (split cores)are coupled to each other.

The rotor 20 includes a rotor core 21 and a permanent magnet 25 attachedto the rotor core 21. The rotor core 21 is made by stacking a pluralityof electromagnetic steel sheets each having a thickness of 0.1 mm to 0.7mm (0.35 mm in this example) in the direction of the rotation axis andfastening the sheets by crimping.

The rotor core 21 has a cylindrical shape, and a shaft hole 27 (centerhole) is formed at a center in the radial direction. A shaft serving asa rotation shaft of the rotor 20 (for example, a shaft 90 of a rotarycompressor 8) is fixed to the shaft hole 27 by shrinkage fitting, pressfitting, or the like.

A plurality of (six in this example) magnet insertion holes 22 in whichthe permanent magnets 25 are inserted are formed along an outerperipheral surface of the rotor core 21. The magnet insertion holes 22are openings, and one magnet insertion hole 22 corresponds to onemagnetic pole. Since the six magnet insertion holes 22 are provided inthis example, the rotor 20 has six poles in total.

The magnet insertion hole 22 has a V shape such that a center portion inthe circumferential direction projects inward in the radial direction inthis example. In this regard, the magnet insertion hole 22 is notlimited to the V shape, but may have a straight shape, for example.

Two permanent magnets 25 are disposed in each magnet insertion hole 22.That is, two permanent magnets 25 are disposed for one magnetic pole. Inthis example, since the rotor 20 has six poles as described above,twelve permanent magnets 25 are disposed in total.

The permanent magnet 25 is a flat-plate member elongated in the axialdirection of the rotor core 21, has a width in the circumferentialdirection of the rotor core 21, and has a thickness in the radialdirection of the rotor core 21. The permanent magnet 25 is constitutedby, for example, a rare earth magnet containing neodymium (Nd), iron(Fe), and boron (B) as main components.

The permanent magnets 25 are magnetized in the thickness direction. Twopermanent magnets 25 disposed in one magnet insertion hole 22 aremagnetized in such a manner that the same magnetic poles face the sameside in the radial direction.

Flux barriers 26 are formed at both ends of the magnet insertion hole 22in the circumferential direction. The flux barriers 26 are openingsformed continuously with the magnet insertion hole 22. The flux barriers26 are provided for reducing leakage magnetic flux between adjacentmagnetic poles (i.e., magnetic flux flowing through inter-pole parts).

In the rotor core 21, a first magnet retention portion 23 that is aprojection is formed at a center of each magnet insertion hole 22 in thecircumferential direction. Further, in the rotor core 21, second magnetretention portions 24 that are projections are formed at both ends ofthe magnet insertion hole 22 in the circumferential direction. The firstmagnet retention portion 23 and the second magnet retention portions 24are provided for positioning and retaining the permanent magnets 25 ineach magnet insertion hole 22.

As described above, the number of slots of the stator 10 (i.e., thenumber of tooth portions 12) is nine, and the number of poles of therotor 20 is six. That is, in the motor 1, a ratio of the number of polesof the rotor 20 to the number of slots of the stator 10 is 2:3.

In the motor 1, the connection state of the coils 3 is switched betweena Y connection and a delta connection. In the case where the deltaconnection is used, a cyclic current may flow and may cause degradationof performance of the motor 1. The cyclic current is caused by a thirdharmonic wave generated in an induced voltage in the winding of eachphase. It is known that in the case of concentrated winding where theratio of the number of poles to the number of slots is 2:3, no thirdharmonic wave is generated in an induced voltage on the assumption thatthere is no influence of magnetic saturation or the like, and thereforeno performance degradation is caused by the cyclic current.

(Configuration of Rotary Compressor)

Next, the rotary compressor 8 using the motor 1 will be described. FIG.2 is a cross-sectional view illustrating a configuration of the rotarycompressor 8. The rotary compressor 8 includes a shell 80, a compressionmechanism 9 disposed in the shell 80, and the motor 1 for driving thecompression mechanism 9. The rotary compressor 8 further includes ashaft 90 (crank shaft) coupling the motor 1 and the compressionmechanism 9 to each other so that a driving force can be transferred.The shaft 90 is fitted in the shaft hole 27 (FIG. 1) of the rotor 20 ofthe motor 1.

The shell 80 is a closed container made of, for example, a steel sheet,and covers the motor 1 and the compression mechanism 9. The shell 80includes an upper shell 80 a and a lower shell 80 b. The upper shell 80a is provided with glass terminals 81 serving as a terminal portion forsupplying electric power from outside of the rotary compressor 8 to themotor 1, and a discharge pipe 85 for discharging refrigerant compressedin the rotary compressor 8 to outside. Here, six lead wires in totalcorresponding to two portions for each of the U-phase, the V-phase, andthe W-phase of the coils 3 of the motor 1 (FIG. 1) are drawn out fromthe glass terminals 81. The lower shell 80 b houses the motor 1 and thecompression mechanism 9.

The compression mechanism 9 has an annular first cylinder 91 and anannular second cylinder 92 along the shaft 90. The first cylinder 91 andthe second cylinder 92 are fixed to an inner peripheral portion of theshell 80 (the lower shell 80 b). An annular first piston 93 is disposedon an inner peripheral side of the first cylinder 91, and an annularsecond piston 94 is disposed on an inner peripheral side of the secondcylinder 92. The first piston 93 and the second piston 94 are rotarypistons that rotate together with the shaft 90.

A partition plate 97 is provided between the first cylinder 91 and thesecond cylinder 92. The partition plate 97 is a disk-shaped memberhaving a through hole at a center thereof. Vanes (not shown) areprovided in cylinder chambers of the first cylinder 91 and the secondcylinder 92 to divide each of the cylinder chambers into a suction sideand a compression side. The first cylinder 91, the second cylinder 92,and the partition plate 97 are integrally fixed using bolts 98.

An upper frame 95 is disposed above the first cylinder 91 so as to closean upper side of the cylinder chamber of the first cylinder 91. A lowerframe 96 is disposed below the second cylinder 92 so as to close a lowerside of the cylinder chamber of the second cylinder 92. The upper frame95 and the lower frame 96 rotatably support the shaft 90.

Refrigerating machine oil (not shown) for lubricating sliding portionsof the compression mechanism 9 is stored at a bottom portion of thelower shell 80 b of the shell 80. The refrigerating machine oil flowsupward through a hole 90 a formed in the axial direction in the shaft 90and is supplied to the sliding portions from oil supply holes 90 bformed at a plurality of positions of the shaft 90.

The stator 10 of the motor 1 is attached to an inner side of the shell80 by shrinkage fitting. Electric power is supplied to the coils 3 ofthe stator 10 from the glass terminals 81 attached to the upper shell 80a. The shaft 90 is fixed to the shaft hole 27 (FIG. 1) of the rotor 20.

An accumulator 87 for storing refrigerant gas is attached to the shell80. The accumulator 87 is held by, for example, a holding portion 80 cprovided on an outer side the lower shell 80 b. A pair of suction pipes88 and 89 are attached to the shell 80, and refrigerant gas is suppliedfrom the accumulator 87 to the cylinders 91 and 92 through the suctionpipes 88 and 89.

As the refrigerant, R410A, R407C, or R22, for example, may be used. Itis preferable to use low global warming potential (GWP) refrigerant fromthe viewpoint of prevention of global warming. As the low GWPrefrigerant, for example, the following refrigerants can be used.

(1) First, a halogenated hydrocarbon having a double bond of carbon inits composition, such as hydro-fluoro-orefin (HFO)-1234yf (CF3CF=CH2)can be used. The GWP of HFO-1234yf is 4.

(2) Further, a hydrocarbon having a double bond of carbon in itscomposition, such as R1270 (propylene), may be used. The GWP of R1270 is3, which is lower than that of HFO-1234yf, but flammability of R1270 ishigher than that of HFO-1234yf.

(3) Further, a mixture containing at least one of a halogenatedhydrocarbon having a double bond of carbon in its composition or ahydrocarbon having a double bond of carbon in its composition, such as amixture of HFO-1234yf and R32, may be used. Since the above describedHFO-1234yf is a low-pressure refrigerant and tends to cause an increasein pressure loss, its use may cause degradation of performance of arefrigeration cycle (especially an evaporator). Thus, it is practicallypreferable to use a mixture with R32 or R41 which is a higher pressurerefrigerant than HFO-1234yf.

A basic operation of the rotary compressor 8 is as follows. Refrigerantgas supplied from the accumulator 87 is supplied to the cylinderchambers of the first cylinder 91 and the second cylinder 92 through thesuction pipes 88 and 89. When the motor 1 is driven and the rotor 20rotates, the shaft 90 rotates together with the rotor 20. Then, thefirst piston 93 and the second piston 94 fitted to the shaft 90 rotateeccentrically in the cylinder chambers and compress the refrigerant inthe cylinder chambers. The compressed refrigerant flows upward in theshell 80 through holes (not shown) provided in the rotor 20 of the motor1 and is discharged to outside through the discharge pipe 85.

(Configuration of Air Conditioner)

Next, the air conditioner 5 including the driving device according tothe first embodiment will be described. FIG. 3 is a block diagramillustrating a configuration of the air conditioner 5. The airconditioner 5 includes an indoor unit 5A placed in a room (airconditioning target space) and an outdoor unit 5B placed outdoors. Theindoor unit 5A and the outdoor unit 5B are connected by connecting pipes40 a and 40 b through which refrigerant flows. Liquid refrigerantpassing through a condenser flows through the connection pipe 40 a. Gasrefrigerant passing through an evaporator flows through the connectionpipe 40 b.

The outdoor unit 5B includes a compressor 41 that compresses anddischarges refrigerant, a four-way valve (refrigerant channel switchingvalve) 42 that switches a flow direction of the refrigerant, an outdoorheat exchanger 43 that exchanges heat between outside air and therefrigerant, and an expansion valve (pressure reducing device) 44 thatdepressurizes high-pressure refrigerant to a low pressure. Thecompressor 41 is constituted by the rotary compressor 8 described above(FIG. 2). The indoor unit 5A includes an indoor heat exchanger 45 thatperforms heat exchange between indoor air and the refrigerant.

The compressor 41, the four-way valve 42, the outdoor heat exchanger 43,the expansion valve 44, and the indoor heat exchanger 45 are connectedby a pipe 40 including the above described connection pipes 40 a and 40b to constitute a refrigerant circuit. These components constitute acompression type refrigeration cycle (compression type heat pump cycle)in which refrigerant is circulated by the compressor 41.

In order to control an operation of the air conditioner 5, an indoorcontroller 50 a is disposed in the indoor unit 5A, and an outdoorcontroller 50 b is disposed in the outdoor unit 5B. Each of the indoorcontroller 50 a and the outdoor controller 50 b has a control board onwhich various circuits for controlling the air conditioner 5 are formed.The indoor controller 50 a and the outdoor controller 50 b are connectedto each other by a communication cable 50 c. The communication cable 50c is bundled together with the connecting pipes 40 a and 40 b describedabove.

In the outdoor unit 5B, an outdoor fan 46 that is a fan is disposed soas to face the outdoor heat exchanger 43. The outdoor fan 46 generatesan air flow passing through the outdoor heat exchanger 43 by rotation.The outdoor fan 46 is constituted by, for example, a propeller fan.

The four-way valve 42 is controlled by the outdoor controller 50 b andswitches the direction of flow of refrigerant. When the four-way valve42 is in the position indicated by the solid line in FIG. 3, gasrefrigerant discharged from the compressor 41 is sent to the outdoorheat exchanger 43 (condenser). When the four-way valve 42 is in theposition indicated by the broken line in FIG. 3, gas refrigerant flowingfrom the outdoor heat exchanger 43 (evaporator) is sent to thecompressor 41. The expansion valve 44 is controlled by the outdoorcontroller 50 b, and changes its opening degree to reduce the pressureof high-pressure refrigerant to a low pressure.

In the indoor unit 5A, an indoor fan 47 that is a fan is disposed so asto face the indoor heat exchanger 45. The indoor fan 47 rotates togenerate an air flow passing through the indoor heat exchanger 45. Theindoor fan 47 is constituted by, for example, a crossflow fan.

In the indoor unit 5A, a room temperature sensor 54 as a temperaturesensor is provided. The room temperature sensor 54 measures a roomtemperature Ta which is an air temperature in the room (air conditioningtarget space), and sends the measured temperature information(information signal) to the indoor controller 50 a. The room temperaturesensor 54 may be constituted by a temperature sensor used in a generalair conditioner. Alternatively, a radiant temperature sensor detecting asurface temperature of, for example, a wall or a floor in the room maybe used.

In the indoor unit 5A, a signal receiving unit 56 that receives aninstruction signal (operation instruction signal) transmitted from aremote controller 55 (remote operation device) operated by a user isalso provided. The remote controller 55 is used by a user to give aninstruction of an operation input (start and stop of operation) oroperation content (set temperature, wind speed, or the like) to the airconditioner 5.

The compressor 41 is configured to change an operating rotation speed ina range from 20 rps to 130 rps during a normal operation. As therotation speed of the compressor 41 increases, a circulation amount ofrefrigerant in the refrigerant circuit increases. The rotation speed ofthe compressor 41 is controlled by the controller 50 (more specifically,the outdoor controller 50 b) in accordance with a temperature differenceΔT between the current room temperature Ta obtained by the roomtemperature sensor 54 and a set temperature Ts set by the user with theremote controller 55. As the temperature difference ΔT increases, thecompressor 41 rotates at a higher rotation speed, and the circulationamount of refrigerant is increased.

Rotation of the indoor fan 47 is controlled by the indoor controller 50a. The rotation speed of the indoor fan 47 can be switched to aplurality of stages. In this example, the rotation speed can be switchedto, for example, three stages of strong wind, middle wind, and softwind. When the wind speed setting is set to an automatic mode with theremote controller 55, the rotation speed of the indoor fan 47 isswitched in accordance with the temperature difference ΔT between themeasured room temperature Ta and the set temperature Ts.

Rotation of the outdoor fan 46 is controlled by the outdoor controller50 b. The rotation speed of the outdoor fan 46 can be switched to aplurality of stages. In this example, the rotation speed of the outdoorfan 46 is switched in accordance with the temperature difference ΔTbetween the measured room temperature Ta and the set temperature Ts.

The indoor unit 5A further includes a lateral wind direction plate 48and a vertical wind direction plate 49. The lateral wind direction plate48 and the vertical wind direction plate 49 change a blowing directionwhen conditioned air subjected to heat exchange in the indoor heatexchanger 45 is blown into the room by the indoor fan 47. The lateralwind direction plate 48 changes the blowing direction laterally, and thevertical wind direction plate 49 changes the blowing directionvertically. An angle of each of the lateral wind direction plate 48 andthe vertical wind direction plate 49, that is, a wind direction of theblown air is controlled by the indoor controller 50 a based on thesetting of the remote controller 55.

A basic operation of the air conditioner 5 is as follows. In a coolingoperation, the four-way valve 42 is switched to a position indicated bythe solid line, and high-temperature and high-pressure gas refrigerantdischarged from the compressor 41 flows into the outdoor heat exchanger43. In this case, the outdoor heat exchanger 43 operates as a condenser.When air passes through the outdoor heat exchanger 43 by rotation of theoutdoor fan 46, heat of condensation of the refrigerant is taken by theair due to heat exchange. The refrigerant is condensed intohigh-pressure and low-temperature liquid refrigerant, and isadiabatically expanded by the expansion valve 44 to become low-pressureand low-temperature two-phase refrigerant.

The refrigerant passing through the expansion valve 44 flows into theindoor heat exchanger 45 of the indoor unit 5A. The indoor heatexchanger 45 operates as an evaporator. When air passes through theindoor heat exchanger 45 by rotation of the indoor fan 47, heat ofvaporization of the air is taken by the refrigerant due to heatexchange, and the cooled air is supplied to the room. The refrigerantevaporates to become low-temperature and low-pressure gas refrigerant,and is compressed again into high-temperature and high-pressurerefrigerant by the compressor 41.

In a heating operation, the four-way valve 42 is switched to a positionindicated by the dotted line, and high-temperature and high-pressure gasrefrigerant discharged from the compressor 41 flows into the indoor heatexchanger 45. In this case, the indoor heat exchanger 45 operates as acondenser. When air passes through the indoor heat exchanger 45 byrotation of the indoor fan 47, heat of condensation is taken from therefrigerant due to heat exchange, and the heated air is supplied to theroom. The refrigerant is condensed into high-pressure andlow-temperature liquid refrigerant, and is adiabatically expanded by theexpansion valve 44 to become low-pressure and low-temperature two-phaserefrigerant.

The refrigerant passing through the expansion valve 44 flows into theoutdoor heat exchanger 43 of the outdoor unit 5B. The outdoor heatexchanger 43 operates as an evaporator. When air passes through theoutdoor heat exchanger 43 by rotation of the outdoor fan 46, heat ofvaporization of the air is taken by the refrigerant due to heatexchange. The refrigerant evaporates to become low-temperature andlow-pressure gas refrigerant, and is compressed again intohigh-temperature and high-pressure refrigerant by the compressor 41.

FIG. 4 is a conceptual diagram showing a basic configuration of acontrol system of the air conditioner 5. The indoor controller 50 a andthe outdoor controller 50 b described above exchange information witheach other through the communication cable 50 c to control the airconditioner 5. In this example, the indoor controller 50 a and theoutdoor controller 50 b are collectively referred to as a controller 50.

FIG. 5(A) is a block diagram showing a control system of the airconditioner 5. The controller 50 is constituted by, for example, amicrocomputer. The controller 50 incorporates an input circuit 51, anarithmetic circuit 52, and an output circuit 53.

The input circuit 51 receives an instruction signal received by thesignal receiving unit 56 from the remote controller 55. The instructionsignal includes, for example, signals for setting an operation input, anoperation mode, a set temperature, an airflow amount, or a winddirection. The input circuit 51 also receives temperature informationindicating a room temperature detected by the room temperature sensor54. The input circuit 51 outputs the received information to thearithmetic circuit 52.

The arithmetic circuit 52 includes a central processing unit (CPU) 57and a memory 58. The CPU 57 performs calculation processing anddetermination processing. The memory 58 stores various set values andprograms for use in controlling the air conditioner 5. The arithmeticcircuit 52 performs calculation and determination based on theinformation received from the input circuit 51, and outputs the resultto the output circuit 53.

Based on the information input from the arithmetic circuit 52, theoutput circuit 53 outputs control signals to the compressor 41, aconnection switching unit 60 (described later), a converter 102, aninverter 103, the compressor 41, the four-way valve 42, the expansionvalve 44, the outdoor fan 46, the indoor fan 47, the lateral winddirection plate 48, and the vertical wind direction plate 49.

As described above, since the indoor controller 50 a and the outdoorcontroller 50 b (FIG. 4) exchange information with each other throughthe communication cable 50 c and control the various devices of theindoor unit 5A and the outdoor unit 5B. Thus, in this example, theindoor controller 50 a and the outdoor controller 50 b are collectivelyreferred to as the controller 50. Practically, each of the indoorcontroller 50 a and the outdoor controller 50 b is constituted by amicrocomputer. It is also possible that a controller is provided in onlyone of the indoor unit 5A and the outdoor unit 5B and controls variousdevices of the indoor unit 5A and the outdoor unit 5B.

FIG. 5(B) is a block diagram showing a section of the controller 50 forcontrolling the motor 1 of the compressor 41 based on the roomtemperature Ta. The arithmetic circuit 52 of the controller 50 includesa received content analysis unit 52 a, a room temperature acquiring unit52 b, a temperature difference calculation unit 52 c, and a compressorcontrol unit 52 d. These components are included in, for example, theCPU 57 of the arithmetic circuit 52.

The received content analysis unit 52 a analyzes an instruction signalinput from the remote controller 55 via the signal reception unit 56 andthe input circuit 51. Based on the analysis result, the received contentanalysis unit 52 a outputs, for example, the operation mode and the settemperature Ts to the temperature difference calculation unit 52 c. Theroom temperature acquiring unit 52 b acquires the room temperature Tainput from the room temperature sensor 54 via the input circuit 51, andoutputs the acquired room temperature Ta to the temperature differencecalculation unit 52 c.

The temperature difference calculation unit 52 c calculates atemperature difference ΔT between the room temperature Ta input from theroom temperature acquiring unit 52 b and the set temperature Ts inputfrom the received content analysis unit 52 a. If the operation modeinput from the received content analysis unit 52 a is the heatingoperation, a temperature difference ΔT=Ts-Ta is calculated. If theoperation mode is the cooling operation, a temperature differenceΔT=Ta−Ts is calculated. The temperature difference calculation unit 52 coutputs the calculated temperature difference ΔT to the compressorcontrol unit 52 d.

Based on the temperature difference ΔT input from the temperaturedifference calculation unit 52 c, the compressor control unit 52 dcontrols the driving device 100 to thereby control the rotation speed ofthe motor 1 (i.e., the rotation speed of the compressor 41).

(Configuration of Driving Device)

Next, the driving device 100 for driving the motor 1 will be described.FIG. 6 is a block diagram illustrating a configuration of the drivingdevice 100. The driving device 100 includes the converter 102 forrectifying an output of a power source 101, the inverter 103 foroutputting an alternating-current voltage to the coils 3 of the motor 1,the connection switching unit 60 for switching the connection state ofthe coils 3, and the controller 50. The converter 102 is supplied withelectric power from the power source 101 that is an alternating-current(AC) power source.

The power source 101 is, for example, an AC power source of 200 V(effective voltage). The converter 102 is a rectifier circuit, andoutputs a direct-current (DC) voltage of, for example, 280 V. Thevoltage output from the converter 102 is referred to as a bus voltage.The inverter 103 is supplied with a bus voltage from the converter 102,and outputs a line voltage (also referred to as a motor voltage) to thecoils 3 of the motor 1. Wires 104, 105, and 106 connected to the coils3U, 3V, and 3W, respectively, are connected to the inverter 103.

The coil 3U has terminals 31U and 32U. The coil 3V has terminals 31V and32V. The coil 3W has terminals 31W and 32W. The wire 104 is connected tothe terminal 31U of the coil 3U. The wire 105 is connected to theterminal 31V of the coil 3V. The wire 106 is connected to the terminal31W of the coil 3W.

The connection switching unit 60 has switches 61, 62, and 63. The switch61 connects the terminal 32U of the coil 3U to either the wire 105 or aneutral point 33. The switch 62 connects the terminal 32V of the coil 3Vto either the wire 106 or the neutral point 33. The switch 63 connectsthe terminal 32W of the coil 3W to either the wire 104 or the neutralpoint 33. The switches 61, 62, and 63 of the connection switching unit60 are constituted by relay contacts in this example. In this regard,the switches 61, 62, and 63 may be constituted by semiconductorswitches.

The controller 50 controls the converter 102, the inverter 103, and theconnection switching unit 60. The configuration of the controller 50 isas described with reference to FIG. 5. The controller 50 receives theoperation instruction signal from the remote controller 55 received bythe signal receiving unit 56 and also receives the room temperaturedetected by the room temperature sensor 54. Based on the receivedinformation, the controller 50 outputs a voltage switching signal to theconverter 102, outputs an inverter driving signal to the inverter 103,and outputs a connection switching signal to the connection switchingunit 60.

In a state shown in FIG. 6, the switch 61 connects the terminal 32U ofthe coil 3U to the neutral point 33, the switch 62 connects the terminal32V of the coil 3V to the neutral point 33, and the switch 63 connectsthe terminal 32W of the coil 3W to the neutral point 33. That is, theterminals 31U, 31V, and 31W of the coils 3U, 3V, and 3W are connected tothe inverter 103, and the terminals 32U, 32V, and 32W are connected tothe neutral point 33.

FIG. 7 is a block diagram illustrating a state where the switches 61,62, and 63 of the connection switching unit 60 in the driving device 100are switched. In the state illustrated in FIG. 7, the switch 61 connectsthe terminal 32U of the coil 3U to the wire 105, the switch 62 connectsthe terminal 32V of the coil 3V to the wire 106, and the switch 63connects the terminal 32W of the coil 3W to the wire 104.

FIG. 8(A) is a schematic diagram illustrating a connection state of thecoils 3U, 3V, and 3W when the switches 61, 62, and 63 are in the stateshown in FIG. 6. The coils 3U, 3V, and 3W are connected to the neutralpoint 33 at the terminals 32U, 32V, and 32W, respectively. Thus, theconnection state of the coils 3U, 3V, and 3W is the Y connection (starconnection).

FIG. 8(B) is a schematic diagram illustrating a connection state of thecoils 3U, 3V, and 3W when the switches 61, 62, and 63 are in the stateshown in FIG. 7. The terminal 32U of the coil 3U is connected to theterminal 31V of the coil 3V via the wire 105 (FIG. 7). The terminal 32Vof the coil 3V is connected to the terminal 31W of the coil 3W via thewire 106 (FIG. 7). The terminal 32W of the coil 3W is connected to theterminal 31U of the coil 3U via the wire 104 (FIG. 7). Thus, theconnection state of the coils 3U, 3V, and 3W is the delta connection.

In this manner, the connection switching unit 60 is capable of switchingthe connection state of the coils 3U, 3V, and 3W of the motor 1 betweenthe Y connection (first connection state) and the delta connection(second connection state) by switching the switches 61, 62, and 63.

FIG. 9 is a schematic diagram illustrating coil portions of the coils3U, 3V, and 3W. As described above, the motor 1 has nine tooth portions12 (FIG. 1), and each of the coils 3U, 3V, and 3W is wound around threetooth portions 12. That is, the coil 3U is obtained by connecting, inseries, U-phase coil portions Ua, Ub, and Uc wound around the threetooth portions 12. Similarly, the coil 3V is obtained by connecting, inseries, V-phase coil portions Va, Vb, and Vc wound around the threetooth portions 12. The coil 3W is obtained by connecting, in series,W-phase coil portions Wa, Wb, and We wound around the three toothportions 12.

(Operation of Air Conditioner)

FIGS. 10 through 12 are flowcharts showing a basic operation of the airconditioner 5. The controller 50 of the air conditioner 5 starts anoperation when the signal reception unit 56 receives a start signal fromthe remote controller 55 (step S101). In this example, the CPU 57 of thecontroller 50 is activated. As will be described later, since theconnection state of the coils 3 is switched to the delta connection whenthe preceding operation of the air conditioner 5 is terminated, theconnection state of the coils 3 is the delta connection when theoperation is started (at start-up).

Next, the controller 50 performs a start process of the air conditioner5 (step S102). Specifically, fan motors of the indoor fan 47 and theoutdoor fan 46 are driven, for example.

Then, the controller 50 outputs a voltage switching signal to theconverter 102 to raise a bus voltage of the converter 102 to a busvoltage (for example, 390 V) corresponding to the delta connection (stepS103). The bus voltage of the converter 102 is the maximum voltageapplied from the inverter 103 to the motor 1.

Then, the controller 50 starts the motor 1 (step S104). Thus, the motor1 is started while the connection state of the coils 3 is set to thedelta connection. Further, the controller 50 controls the output voltageof the inverter 103 to control the rotation speed of the motor 1.

Specifically, the controller 50 increases the rotation speed of themotor 1 stepwise at a preset speed in accordance with the temperaturedifference ΔT. An allowable maximum rotation speed of the rotation speedof the motor 1 is, for example, 130 rps. As a result, the amount ofrefrigerant circulated by the compressor 41 is increased, and a coolingcapacity is increased in the case of the cooling operation whereas aheating capacity is increased in the case of the heating operation.

Further, when the room temperature Ta approaches the set temperature Tsdue to air conditioning effect and the temperature difference ΔT shows adecreasing tendency, the controller 50 reduces the rotation speed of themotor 1 in accordance with the temperature difference ΔT. When thetemperature difference ΔT decreases to a preset temperature near zero(but larger than zero), the controller 50 operates the motor 1 at anallowable minimum rotation speed (for example, 20 rps).

Further, when the temperature Ta reaches the set temperature Ts (i.e.,when the temperature difference ΔT is zero or less), the controller 50stops rotation of the motor 1 in order to prevent overcooling (oroverheating). Accordingly, the compressor 41 is stopped. Then, when thetemperature difference ΔT becomes larger than zero again, the controller50 restarts rotation of the motor 1. The controller 50 restricts restartof rotation of the motor 1 in a short time period so as not to repeatrotation and stop of the motor 1 in a short time period.

When the rotation speed of the motor 1 reaches a preset rotation speed,the inverter 103 starts field-weakening control. The field-weakeningcontrol will be described later with reference to FIGS. 15 through 30.

The controller 50 determines whether or not an operation stop signal(signal to stop an operation of the air conditioner 5) is received fromthe remote controller 55 through the signal receiving unit 56 (stepS105). If the operation stop signal is not received, the controller 50proceeds to step S106. If the operation stop signal is received, thecontroller 50 proceeds to step S109.

The controller 50 acquires the temperature difference ΔT between theroom temperature Ta detected by the room temperature sensor 54 and theset temperature Ts set by the remote controller (step S106). Based onthe temperature difference ΔT, the controller 50 determines whetherswitching of the connection state of the coils 3 from the deltaconnection to the Y connection is necessary or not. That is, it isdetermined whether or not the connection state of the coils 3 is thedelta connection and an absolute value of the temperature difference ΔTis less than or equal to a threshold ΔTr (step S107). The threshold ΔTris a temperature difference corresponding to an air-conditioning load(also referred to simply as “load”) that is small enough to performswitching to the Y connection.

As described above, ΔT is represented as ΔT=Ts−Ta when the operationmode is the heating operation and is represented as ΔT=Ta−Ts when theoperation is the cooling operation. Thus, in this example, the absolutevalue of ΔT and the threshold ΔTr are compared to each other todetermine whether switching to the Y connection is necessary or not.

If the result of the comparison in step S107 indicates that theconnection state of the coils 3 is the delta connection and the absolutevalue of the temperature difference ΔT is less than or equal to thethreshold ΔTr, the process proceeds to step S121 (FIG. 11).

As shown in FIG. 11, in step S121, the controller 50 outputs a stopsignal to the inverter 103 to stop rotation of the motor 1. Thereafter,the controller 50 outputs the connection switching signal to theconnection switching unit 60, and switches the connection state of thecoils 3 from the delta connection to the Y connection (step S122).Subsequently, the controller 50 outputs a voltage switching signal tothe converter 102 to lower the bus voltage of the converter 102 to avoltage (280 V) corresponding to the Y connection (step S123), andrestarts rotation of the motor 1 (step S124). Thereafter, the processreturns to step S105 described above (FIG. 10).

If the result of the comparison in step S107 indicates that theconnection state of the coils 3 is not the delta connection (if it isthe Y connection), or that the absolute value of the temperaturedifference ΔT is larger than the threshold ΔTr (i.e., if switching tothe Y connection is unnecessary), the process proceeds to step S108.

In step S108, it is determined whether switching from the Y connectionto the delta connection is necessary or not. That is, it is determinedwhether or not the connection state of the coils 3 is the Y connectionand the absolute value of the temperature difference ΔT described aboveis larger than the threshold ΔTr.

If the result of the comparison in step S108 indicates that theconnection state of the coils 3 is the Y connection and the absolutevalue of the temperature difference ΔT is larger than the threshold ΔTr,the process proceeds to step S131 (FIG. 12).

As shown in FIG. 12, in step S131, the controller 50 stops rotation ofthe motor 1. Thereafter, the controller 50 outputs the connectionswitching signal to the connection switching unit 60, and switches theconnection state of the coils 3 from the Y connection to the deltaconnection (step S132). Subsequently, the controller 50 outputs thevoltage switching signal to the converter 102 to raise the bus voltageof the converter 102 to the voltage (390 V) corresponding to the deltaconnection (step S133), and restarts rotation of the motor 1 (S134).

In the case of the delta connection, the motor 1 can be driven to ahigher rotation speed as compared to the case of the Y connection, andthus it is possible to respond to a larger load. It is thereforepossible to converge the temperature difference ΔT between the roomtemperature and the set temperature in a short time period. Thereafter,the process returns to step S105 described above (FIG. 10).

If the result of the comparison in step S108 indicates that theconnection state of the coils 3 is not the Y connection (i.e., if it isthe delta connection), or that the absolute value of the temperaturedifference ΔT is less than or equal to the threshold ΔTr (i.e., ifswitching to the delta connection is unnecessary), the process returnsto step S105.

If the operation stop signal is received in step S105 described above,rotation of the motor 1 is stopped (step S109). Thereafter, thecontroller 50 switches the connection state of the coils 3 from the Yconnection to the delta connection (step S110). If the connection stateof the coils 3 is already the delta connection, the connection state isunchanged. In this regard, although not shown in FIG. 10, if theoperation stop signal is received in steps S106 through S108, theprocess proceeds to step S109 and rotation of the motor 1 is stopped.

Thereafter, the controller 50 performs a stop process of the airconditioner 5 (step S111). Specifically, the fan motors of the indoorfan 47 and the outdoor fan 46 are stopped. Thereafter, the CPU 57 of thecontroller 50 is stopped, and the operation of the air conditioner 5 isterminated.

As described above, if the absolute value of the temperature differenceΔT between the room temperature Ta and the set temperature Ts isrelatively small (i.e., if the absolute value is less than or equal tothe threshold ΔTr), the motor 1 is operated using the Y connectionachieving high efficiency. If it is necessary to respond to a largerload, that is, if the absolute value of the temperature difference ΔT islarger than the threshold ΔTr, the motor 1 is operated using the deltaconnection enabling responding to a larger load. Accordingly, theoperation efficiency of the air conditioner 5 can be enhanced.

In this regard, in the switching operation from the Y connection to thedelta connection (FIG. 12), as shown in FIG. 13(A), it is also possibleto detect the rotation speed of the motor 1 (step S135) and to determinewhether or not the detected rotation speed is greater than or equal to athreshold (reference value of rotation speed) (step S136), before step131 in which the rotation of the motor 1 is stopped. The rotation speedof the motor 1 is detected as a frequency of an output current of theinverter 103.

In step S136, a rotation speed of 60 rps is used as a threshold of therotation speed of the motor 1. The rotation speed of 60 rps isintermediate between a rotation speed of 35 rps corresponding to anintermediate heating condition described later and a rotation speed of85 rps corresponding to a rated heating condition. If the rotation speedof the motor 1 is greater than or equal to the threshold, rotation ofthe motor 1 is stopped and switching to the delta connection isperformed, and the bus voltage of the converter 102 is raised (stepsS131, S132, and S133). If the rotation speed of the motor 1 is less thanthe threshold, the process returns to step S105 in FIG. 10.

As above, in addition to the determination on whether the connectionswitching is necessary or not based on the temperature difference ΔT(step S108), the determination on whether the connection switching isnecessary or not is performed based on the rotation speed of the motor1. Thus, frequent repetition of connection switching can be sufficientlysuppressed.

Further, as shown in FIG. 13(B), it is also possible to detect an outputvoltage of the inverter 103 (step S137), and to determine whether or notthe detected output voltage is greater than or equal to a threshold(reference value of the output voltage) (step S138), before step S131 inwhich rotation of the motor 1 is stopped.

FIGS. 13(A) and 13(B) show the switching operations from the Yconnection to the delta connection. However, determination based on therotation speed of the motor 1 or the output voltage of the inverter 103may be performed when the switching from the delta connection to the Yconnection is performed.

FIG. 14 is a timing chart showing an example of an operation of the airconditioner 5. FIG. 14 shows an operation state of the air conditioner 5and driving states of the outdoor fan 46 and the motor 1 (compressor41). The outdoor fan 46 is shown as an example of components other thanthe motor 1 of the air conditioner 5.

When the signal receiving unit 56 receives an operation start signal (ONcommand) from the remote controller 55, the CPU 57 is activated, and theair conditioner 5 is brought into an active state (ON state). The fanmotor of the outdoor fan 46 starts rotating when a time t0 elapses afterthe air conditioner 5 is brought into the active state. The time t0 is adelay time due to communication between the indoor unit 5A and theoutdoor unit 5B.

Rotation of the motor 1 using the delta connection is started when atime t1 elapses after the air conditioner 5 is brought into the activestate. The time t1 is a waiting time until rotation of the fan motor ofthe outdoor fan 46 is stabilized. By rotating the outdoor fan 46 beforerotation of the motor 1 starts, a temperature of the refrigeration cyclecan be prevented from rising higher than necessary.

In the example of FIG. 14, switching from the delta connection to the Yconnection is performed, then switching from the Y connection to thedelta connection is performed, and subsequently the operation stopsignal (OFF instruction) is received from the remote controller 55. Atime t2 necessary for switching the connection is a waiting timenecessary for restarting the motor 1 and is set at a time necessaryuntil a refrigerant pressure in the refrigeration cycle becomessubstantially uniform.

When the operation stop signal is received from the remote control 55,rotation of the motor 1 is stopped. Then, rotation of the fan motor ofthe outdoor fan 46 is stopped when a time t3 elapses after the motor 1is stopped. The time t3 is a waiting time necessary for the temperatureof the refrigeration cycle to sufficiently decrease. Then, the CPU 57stops when a time t4 elapses, and the air conditioner 5 is brought intoan operation stop state (OFF state). The time t4 is a preset waitingtime.

(Connection Switching Based on Temperature Detection)

In the foregoing operation of the air conditioner 5, determination onwhether switching of the connection state of the coils 3 is necessary ornot (steps S107 and S108) may be performed based on, for example, therotation speed of the motor 1 or the inverter output voltage. However,since the rotation speed of the motor 1 may fluctuate in a short timeperiod, it is necessary to determine whether a state where the rotationspeed is less than or equal to a threshold (or greater than or equal tothe threshold) continues for a certain time period. The same applies tothe inverter output voltage.

In particular, in a case where the set temperature by the remotecontroller 55 is greatly changed, or in a case where the load of the airconditioner 5 rapidly changes due to opening of a window of the room orthe like, there may be a delay until the operation state of thecompressor 41 responds to the load change if it takes time to determinewhether switching of the connection state is necessary or not. As aresult, comfort provided by the air conditioner 5 may deteriorate.

Meanwhile, in this embodiment, the temperature difference ΔT (absolutevalue) between the room temperature Ta detected by the room temperaturesensor 54 and the set temperature Ts is compared to the threshold. Sincefluctuation in temperature is small in a short time period, it is notnecessary to continue the detection of the temperature difference ΔT andthe comparison to the threshold, and thus it is possible to determinewhether switching of the connection is necessary or not in a short timeperiod. Accordingly, the operation state of the compressor 41 canquickly respond to the load change, and comfort provided by the airconditioner 5 can be enhanced.

In the operation of the air conditioner 5 described above, determinationon whether switching from the delta connection to the Y connection isnecessary or not (step S107) and determination on whether switching fromthe Y connection to the delta connection is necessary or not (step S108)are consecutively performed. However, switching from the deltaconnection to the Y connection is performed when the air-conditioningload is decreasing (when the room temperature is approaching the settemperature), and the air-conditioning load is less likely to rapidlyincrease after that. Thus, it is unlikely that the connection switchingis frequently performed.

Further, in the operation of the air conditioner 5 described above,switching of the connection state of the coils 3 (steps S122 and S132)is performed in a state where rotation of the motor is stopped (i.e., astate where the inverter 103 stops outputting). Although switching ofthe connection state of the coils 3 may be performed in a state whereelectric power is continuously supplied to the motor 1, it is preferableto perform switching in a state where the power supply to the motor 1 isstopped, from the viewpoint of reliability of relay contactsconstituting the switches 61, 62, and 63 (FIG. 6) of the connectionswitching unit 60.

In this regard, it is also possible to perform switching of theconnection state of the coils 3 in a state where the rotation speed ofthe motor 1 is sufficiently reduced, and then to return the rotationspeed to the original rotation speed.

Further, the switches 61, 62 and 63 of the connection switching unit 60are constituted by relay contacts in this example. If the switches areconstituted by semiconductor switches, however, it is unnecessary tostop rotation of the motor 1 when the connection state of the coils 3 isswitched.

Further, the connection state of the coils 3 may be switched when astate in which the temperature difference ΔT (absolute value) betweenthe room temperature Ta and the set temperature Ts is less than or equalto the threshold ΔTr is repeated a plurality of times (a preset numberof times). This suppresses repetition of connection switching due tosmall temperature changes.

In this regard, when the temperature difference ΔT between the roomtemperature and the set temperature becomes zero or less (ΔT≤0), thecontroller 50 stops rotation of the motor 1 in order to preventovercooling (overheating) as described above. The connection state ofthe coils 3 may be switched from the delta connection to the Yconnection at this timing. Specifically, whether or not the temperaturedifference ΔT is less than or equal to zero may be determined at stepS107 described above, and if the temperature difference ΔT is less thanor equal to zero, rotation of the motor 1 may be stopped and theconnection state of the coils 3 may be switched to the Y connection.

Further, in the operation of the air conditioner 5 described above,since the bus voltage of the converter 102 is raised when switching fromthe Y connection to the delta connection is performed, high torque canbe generated by the motor 1. Thus, the difference ΔT between the roomtemperature and the set temperature can be converged in a shorter timeperiod. The raising of the bus voltage of the converter 102 will bedescribed later.

(Regarding Connection State at Start-Up)

As described above, when the air conditioner 5 according to the firstembodiment receives the operation start signal and starts the motor 1,the air conditioner 5 starts control while the connection state of thecoils 3 is set to the delta connection. Further, when the operation ofthe air conditioner 5 is terminated, the connection state of the coils 3is switched to the delta connection.

It is difficult to accurately detect an air-conditioning load when theair conditioner 5 starts operation. In particular, when the airconditioner 5 starts operation, the difference between the roomtemperature and the set temperature is generally large and theair-conditioning load is generally large. Thus, in the first embodiment,the motor 1 is started while the connection state of the coils 3 is setto the delta connection capable of responding to a larger load (i.e.,capable of rotating to a higher rotation speed). Accordingly, it ispossible to converge the difference ΔT between the room temperature Taand the set temperature Ts in a shorter time period when the airconditioner 5 starts operation.

Further, even in a case where the air conditioner 5 stops for a longtime period, and an abnormality (for example, inoperability of relays ofthe switches 61 through 63 due to sticking, or the like) occurs in theconnection switching unit 60 during the stop, the motor 1 can be startedwith the delta connection since switching from the Y connection to thedelta connection is performed before termination of the operation of theair conditioner 5. Accordingly, degradation of performance of the airconditioner 5 can be prevented, and comfort is not impaired.

In this regard, in a case where the motor 1 is started while theconnection state of the coils 3 is set to the delta connection andswitching to the Y connection is not performed, it is possible to obtainmotor efficiency equal to that of a general motor in which theconnection state of coils is fixed to the delta connection (i.e., havingno connection switching function).

(Motor Efficiency and Motor Torque)

Next, improvements of motor efficiency and motor torque will bedescribed. In general, household air conditioners are subject to EnergyConservation Act, and it is mandatory to reduce CO₂ emissions from theviewpoint of global environments. With the advance of technology,compression efficiency of compressors, operation efficiency of motors ofthe compressors, heat transfer coefficient of heat exchangers and thelike have been improved, a coefficient of performance (COP) of energyconsumption efficiency of the air conditioners has been increased yearby year, and running costs (power consumption) and CO₂ emissions of theair conditioners have also been reduced.

The COP is used for evaluating performance in the case of operationunder a certain temperature condition, and an operating condition of theair conditioner for each season is not taken into consideration.However, when the air conditioner is actually used, capacity and powerconsumption necessary for cooling or heating change with a change inoutdoor air temperature. Thus, in order to perform evaluation in a stateclose to actual use, an annual performance factor (APF) is used as anindex of energy saving. The APF is efficiency obtained by determining acertain model case, and calculating a total load and a total electricpower consumption throughout the year.

In particular, in the inverter motor, which is a current mainstream, thecapacity varies depending on the rotation speed of the compressor, andthus there is a problem in performing evaluation close to actual useonly under the rated condition.

The APF of a household air conditioner is obtained by calculating apower consumption amount in accordance with annual total load at fiveevaluation points: a rated cooling condition, an intermediate coolingcondition, a rated heating condition, an intermediate heating condition,and a low heating temperature. As the calculated amount is larger,energy saving performance is evaluated to be higher.

As a breakdown of the annual total load, the ratio of the intermediateheating condition is very large (50%), and the ratio of the ratedheating condition is the next largest (25%). Thus, it is effective inenhancing energy saving performance of air conditioners to increasemotor efficiency under the intermediate heating condition and the ratedheating condition.

The rotation speed of a motor of a compressor under evaluation loadconditions of the APF varies depending on a capacity of an airconditioner and performance of a heat exchanger. For example, in ahousehold air conditioner having a refrigeration capacity of 6.3 kW, arotation speed N1 (first rotation speed) under the intermediate heatingcondition is 35 rps, and a rotation speed N2 (second rotation speed)under the rated heating condition is 85 rps.

The motor 1 according to this embodiment is intended to obtain highmotor efficiency and high motor torque at the rotation speed N1corresponding to the intermediate heating condition and the rotationspeed N2 corresponding to the rated heating condition. That is, out ofthe two load conditions for which performance is to be improved, therotation speed at a low-speed side is N1 and the rotation speed at ahigh-speed side is N2.

In the motor 1 in which the permanent magnets 25 are mounted on therotor 20, when the rotor 20 rotates, the magnetic fluxes of thepermanent magnets 25 interlink with the coils 3 of the stator 10, and aninduced voltage is generated in the coils 3. The induced voltage isproportional to the rotation speed (rotation velocity) of the rotor 20and is also proportional to the number of turns of each coil 3. As therotation speed of the motor 1 increases and the number of turns of thecoil 3 increases, the induced voltage increases.

The line voltage (motor voltage) output from the inverter 103 is equalto a sum of the induced voltage and a voltage generated by a resistanceand an inductance of the coils 3. The resistance and the inductance ofthe coils 3 are negligibly small as compared to the induced voltage, andthus the line voltage is practically dominated by the induced voltage. Amagnet torque of the motor 1 is proportional to the product of theinduced voltage and a current flowing through the coils 3.

As the number of turns of the coil 3 increases, the induced voltageincreases. Thus, as the number of turns of the coil 3 increases, acurrent for generating a necessary magnet torque decreases.Consequently, a conduction loss of the inverter 103 can be reduced, andoperation efficiency of the motor 1 can be enhanced. Meanwhile, sincethe induced voltage increases, the line voltage dominated by the inducedvoltage reaches an inverter maximum output voltage (i.e., a bus voltagesupplied from the converter 102 to the inverter 103) at a lower rotationspeed, and the rotation speed cannot be increased higher than that.

Further, when the number of turns of the coil 3 is reduced, the inducedvoltage decreases and the line voltage dominated by the induced voltagedoes not reach the inverter maximum output voltage even at a higherrotation speed, and high-speed rotation is made possible. However, sincethe induced voltage decreases, the current for generating the necessarymagnet torque increases, and thus the conduction loss of the inverter103 increases, so that operation efficiency of the motor 1 decreases.

Further, from the viewpoint of the switching frequency of the inverter103, a harmonic component caused by an ON/OFF duty of switching of theinverter 103 decreases as the line voltage is closer to the invertermaximum output voltage, and thus an iron loss caused by the highharmonic component of the current can be reduced.

FIGS. 15 and 16 are graphs each showing a relationship between the linevoltage and the rotation speed in the motor 1. The connection state ofthe coils 3 is the Y connection. The line voltage is proportional to theproduct of a field magnetic field and a rotation speed. If the fieldmagnetic field is constant, the line voltage and the rotation speed areproportional as shown in FIG. 15. In this regard, in FIG. 15, therotation speed N1 corresponds to the intermediate heating condition, andthe rotation speed N2 corresponds to the rated heating condition.

The line voltage increases as the rotation speed increases. However, asshown in FIG. 16, when the line voltage reaches the inverter maximumoutput voltage, the line voltage cannot be increased higher than that,and thus field-weakening control by the inverter 103 is started. In thisexample, it is assumed that the field-weakening control is started at arotation speed between the rotation speeds N1 and N2.

In the field-weakening control, the induced voltage is weakened bycausing a current having a d-axis phase (in a direction of cancelingmagnetic fluxes of the permanent magnets 25) to flow in the coils 3.This current will be referred to as a weakening current. Since theweakening current is needed to flow in addition to a usual current forgenerating motor torque, a copper loss due to the resistance of thecoils 3 increases, and the conduction loss of the inverter 103 alsoincreases.

FIG. 17 is a graph showing a relationship between the motor efficiencyand the rotation speed in a case where the field-weakening control shownin FIG. 16 is performed. As shown in FIG. 17, the motor efficiencyincreases as the rotation speed increases, and immediately after thefield-weakening control starts, the motor efficiency reaches its peak asindicated by an arrow P.

When the rotation speed further increases, the weakening current flowingin the coils 3 also increases, and thus the copper loss increasesaccordingly so that the motor efficiency decreases. In the overallefficiency that is the product of the motor efficiency and the inverterefficiency, a change represented by a curve similar to that in FIG. 17is observed.

FIG. 18 is a graph showing a relationship between the maximum torque andthe rotation speed of the motor in a case where the field-weakeningcontrol shown in FIG. 16 is performed. Before the field-weakeningcontrol is started, the maximum torque of the motor is constant (due to,for example, restriction by a current threshold). When thefield-weakening control is started, the maximum torque of the motor 1decreases as the rotation speed increases. The maximum torque of themotor 1 is set to be larger than a load (necessary load) actuallygenerated by the motor 1 when a product is used. Hereinafter, themaximum torque of the motor will be referred to as motor torque, forconvenience of description.

FIG. 19 is a graph showing relationships between the line voltage andthe rotation speed for the Y connection and the delta connection. In acase where the connection state of the coils 3 is the delta connection,a phase impedance of the coils 3 is 1/√3 times as large as a phaseimpedance in a case where the connection state of the coils 3 is the Yconnection, suppose that the number of turns is the same in each case.Thus, the line voltage (chain line) in the case where the connectionstate of the coils 3 is the delta connection is 1/√3 times as high asthe line voltage (solid line) in the case where the connection state ofthe coils 3 is the Y connection, suppose that the rotation speed is thesame in each case.

That is, when the coils 3 are connected in the delta connection, if thenumber of turns is made √3 times as large as the number of turns in thecase of the Y connection, the line voltage (motor voltage) is equivalentto that in the case of the Y connection for the same rotation speed N.Thus, an output current of the inverter 103 is also equivalent to thatin the case of the Y connection.

In motors in which the number of turns around each tooth is several tensor more, the Y connection is more often used than the delta connectionfor the following reasons. One reason is that the number of turns ofeach coil in the delta connection is larger than that in the Yconnection, and thus the time necessary for winding the coils is longerin a manufacturing process. Another reason is that there is apossibility that a circulating current may occur in the case of thedelta connection.

In general, in a motor employing the Y connection, the number of turnsof the coil is adjusted such that the line voltage (motor voltage)reaches the inverter maximum output voltage at the rotation speed N2(i.e., the rotation speed at the high-speed side of the rotation speedsfor which performance is to be enhanced). In this case, however, themotor is operated with the line voltage lower than the inverter maximumoutput voltage at the rotation speed N1 (i.e., the rotation speed at thelow-speed side of the rotation speeds for which performance is to beenhanced), and thus it is difficult to obtain high motor efficiency.

Thus, the connection state of the coils is set to the Y-connection, thenumber of turns is adjusted such that the line voltage reaches theinverter maximum output voltage at a rotation speed slightly lower thanthe rotation speed N1, and control is performed to switch the connectionstate of the coils to the delta connection before the motor reaches therotation speed N2.

FIG. 20 is a graph showing a relationship between the line voltage andthe rotation speed in the case where switching from the Y connection tothe delta connection is performed. In the example shown in FIG. 20, whenthe motor reaches a rotation speed (hereinafter referred to as arotation speed N11) slightly lower than the rotation speed N1(intermediate heating condition), the field-weakening control describedabove is started. When the rotation speed N further increases andreaches a rotation speed NO, switching from the Y connection to thedelta connection is performed. Here, the rotation speed N11 is 5% lowerthan the rotation speed N1 (i.e., N11=N1×0.95).

By switching to the delta connection, the line voltage decreases to be1/√3 times as high as that in the Y connection, and thus the degree offield-weakening can be reduced (i.e., the weakening current can bereduced). Accordingly, a copper loss due to the weakening current can bereduced, and decreases in motor efficiency and motor torque can besuppressed.

FIG. 21 is a graph showing relationships between the motor efficiencyand the rotation speed for the Y connection and the delta connection. Asdescribed above, the connection state of the coils 3 is the Y connectionand the number of turns is adjusted such that the line voltage reachesthe inverter maximum output voltage at the rotation speed N11 slightlylower than the rotation speed N1. Thus, as indicated by the solid linein FIG. 21, high motor efficiency can be obtained at the rotation speedN1.

Meanwhile, in the case of the delta connection, motor efficiency higherthan that in the Y connection can be obtained at the rotation speed N2as indicated by the chain line in FIG. 21, suppose that the number ofturns of the coil 3 is the same. Thus, by switching from the Yconnection to the delta connection at an intersection of the solid lineand the chain line shown in FIG. 21, high motor efficiency can beobtained at both of the rotation speed N1 (intermediate heatingcondition) and the rotation speed N2 (rated heating condition).

Thus, as described with reference to FIG. 20, the connection state ofthe coils 3 is set to the Y connection, the number of turns is adjustedsuch that the line voltage reaches the inverter maximum output voltageat the rotation speed N11 (rotation speed slightly lower than therotation speed N1), and control is performed to switch from the Yconnection to the delta connection at the rotation speed NO higher thanthe rotation speed N1.

However, motor efficiency cannot be sufficiently enhanced by simplyswitching the connection state of the coils 3 from the Y connection tothe delta connection. This will be described below.

FIG. 22 is a graph showing a relationship between the motor efficiencyand the rotation speed in a case (solid line) where the connection stateof the coils 3 is the Y connection, the number of turns is adjusted suchthat the line voltage reaches the inverter maximum output voltage at therotation speed N11, and switching from the Y connection to the deltaconnection is performed at the rotation speed NO. The broken line showsa relationship between the motor efficiency and the rotation speed in acase where field-weakening control is performed while the connectionstate of the coils 3 is set to the Y-connection as shown in FIG. 17.

The line voltage is proportional to the rotation speed. For example, ina household air conditioner having a refrigeration capacity of 6.3 kW,the rotation speed N1 (intermediate heating condition) is 35 rps and therotation speed N2 (rated heating condition) is 85 rps, and thus the linevoltage in the rated heating condition is 2.4 times (=85/35) as high asthe line voltage in the intermediate heating condition.

The line voltage in the rated heating condition (rotation speed N2)after the connection state of the coils 3 is switched to the deltaconnection is 1.4 times (=85/35/√3) as high as the inverter maximumoutput voltage. Since the line voltage cannot be made larger than theinverter maximum output voltage, the field-weakening control is started.

In the field-weakening control, the weakening current necessary forweakening the field flows in the coils 3, and thus the copper lossincreases and the motor efficiency and the motor torque decrease.Consequently, as indicated by the solid line in FIG. 22, the motorefficiency in the rated heating condition (rotation speed N2) cannot beimproved.

In order to reduce the degree of field weakening in the rated heatingcondition (rotation speed N2) (i.e., to reduce a weakening current), itis necessary to reduce the line voltage by reducing the number of turnsof the coils 3. In this case, the line voltage in the intermediateheating condition (rotation speed N1) also decreases, and the improvingeffect of the motor efficiency by switching the connection decreases.

That is, if there are two load conditions for which performance is to beimproved and the rotation speed N1 at the low-speed side and therotation speed N2 at the high-speed side satisfy (N2/N1)>√3, thefield-weakening control is necessary even when switching from the Yconnection to the delta connection is performed. Thus, sufficientimproving effect of the motor efficiency cannot be obtained by simplyperforming switching from the Y connection to the delta connection.

FIG. 23 is a graph showing relationships between the motor torque andthe rotation speed for the Y connection and the delta connection. In thecase of the Y connection, as described with reference to FIG. 18, themotor torque is constant with respect to an increase in the rotationspeed N, but when the field-weakening control is started, the motortorque decreases as the rotation speed N increases. In the case of thedelta connection, the field-weakening control is started at a higherrotation speed than that in the case of the Y connection (N11), but whenthe field-weakening control is started, the motor torque decreases asthe rotation speed N increases.

FIG. 24 is a graph showing a relationship between the motor torque andthe rotation speed in a case where the connection state of the coils 3is the Y connection, the number of turns is adjusted such that the linevoltage reaches the inverter maximum output voltage at the rotationspeed N11 (rotation speed slightly lower than the rotation speed N1),and switching from the Y connection to the delta connection is performedat the rotation speed NO higher than the rotation speed N1. As shown inFIG. 24, when the rotation speed reaches the rotation speed N11 and thefield-weakening control is started, the motor torque decreases as therotation speed N increases.

When the rotation speed further increases to reach the rotation speed NOand switching from the Y connection to the delta connection isperformed, the field-weakening control temporarily stops, and thus themotor torque increases. However, when the rotation speed N furtherincreases and the field-weakening control is started, the motor torquedecreases as the rotation speed N increases. In this manner, simplyswitching from the Y connection to the delta connection is not enough tosuppress a decrease in the motor torque especially in a high rotationspeed range.

Thus, the driving device 100 according to the first embodiment switchesthe bus voltage by the converter 102, in addition to switching of theconnection state of the coils 3 by the connection switching unit 60. Theconverter 102 is supplied with a power supply voltage (200 V) from thepower source 101 and supplies the bus voltage to the inverter 103. Theconverter 102 is preferably constituted by an element exhibiting a smallloss due to an increase in voltage (voltage rising), such as a SiCelement or a GaN element.

Specifically, a bus voltage V1 (first bus voltage) when the connectionstate of the coils 3 is the Y connection is set to 280 V (DC).Meanwhile, a bus voltage V2 (second bus voltage) when the connectionstate of the coils 3 is the delta connection is set to 390 V (DC). Thatis, the bus voltage V2 in the case of the delta connection is set to 1.4times as high as the bus voltage V1 in the case of the Y connection. Inthis regard, it is sufficient that the bus voltage V2 satisfiesV2≥(V1/√3)×N2/N1 in relation to the bus voltage V1. The inverter 103supplied with the bus voltage from the converter 102 supplies the linevoltage to the coils 3. The inverter maximum output voltage is 1/√2 ofthe bus voltage.

FIG. 25 is a graph showing relationships between the line voltage andthe rotation speed in a case where the bus voltage is switched by theconverter 102 for the Y connection and the delta connection. As shown inFIG. 25, the line voltage (solid line) in the case where the connectionstate of the coils 3 is the Y connection is 1/√2 (i.e., V1×1/√2) of thebus voltage V1 at maximum. The line voltage (chain line) in the casewhere the connection state of the coils 3 is the delta connection is1/√2 (i.e., V2×1/√2) of the bus voltage V2 at maximum.

FIG. 26 is a graph showing a relationship between the line voltage andthe rotation speed in a case where the connection state is switched bythe connection switching unit 60 and the bus voltage is switched by theconverter 102. As shown in FIG. 26, in a rotation speed range includingthe rotation speed N1 (intermediate heating condition), the connectionstate of the coils 3 is the Y connection. As the rotation speedincreases, the line voltage increases, and the line voltage reaches theinverter maximum output (V1×1/√2) at the rotation speed N11 slightlylower than the rotation speed N1. Thus, the field-weakening control isstarted.

When the rotation speed further increases to reach the rotation speedNO, the connection switching unit 60 switches the connection state ofthe coils 3 from the Y connection to the delta connection. At the sametime, the converter 102 raises the bus voltage from V1 to V2. As the busvoltage is raised, the inverter maximum output becomes V2×1/√2. At thispoint of time, the line voltage is lower than the inverter maximumoutput, and thus the field-weakening control is not performed.

Thereafter, the line voltage increases as the rotation speed Nincreases, the line voltage reaches the inverter maximum output(V2×1/√2) at a rotation speed N21 slightly lower than the rotation speedN2 (rated heating condition), and the field-weakening control isstarted. In this regard, the rotation speed N21 is 5% lower than therotation speed N2 (i.e., N21=N2×0.95).

In the first embodiment, the connection state of the coils 3 is switchedbased on the result of comparison between the temperature difference ΔTbetween the room temperature Ta and the set temperature Ts and thethreshold ΔTr, as described above. Switching from the Y connection tothe delta connection at the rotation speed NO corresponds to theswitching from the Y connection to the delta connection shown in stepS108 in FIG. 10 and steps S131 through S134 in FIG. 12.

The improving effect of the motor efficiency in this case will bedescribed. FIG. 27 is a graph showing relationships between the motorefficiency and the rotation speed for the Y connection and the deltaconnection. In FIG. 27, the motor efficiency (solid line) in the casewhere the connection state of the coils 3 is the Y connection is similarto the motor efficiency in the case of the Y connection shown in FIG.21. Meanwhile, the motor efficiency (chain line) in the case where theconnection state of the coils 3 is the delta connection is higher thanthe motor efficiency in the delta connection shown in FIG. 21 because ofan increase in the bus voltage of the converter 102.

FIG. 28 is a graph showing a relationship between the motor efficiencyand the rotation speed in a case where the connection state is switchedby the connection switching unit 60 and the bus voltage is switched bythe converter 102. Since the connection state of the coils 3 is the Yconnection and the number of turns is set such that the line voltagereaches the inverter maximum output voltage at the rotation speed N11(rotation speed slightly lower than the rotation speed N1), high motorefficiency can be obtained in a rotation speed range including therotation speed N1.

When the rotation speed reaches the rotation speed N11, thefield-weakening control is started. When the rotation speed then reachesthe rotation speed NO, the connection state of the coils 3 is switchedfrom the Y connection to the delta connection, and the bus voltage isincreased by the converter 102.

Since the inverter maximum output voltage increases with an increase inthe bus voltage, the line voltage becomes lower than the invertermaximum output voltage, and accordingly the field-weakening control isstopped. As the field-weakening control is stopped, a copper loss causedby the weakening current is reduced, and thus the motor efficiencyincreases.

Thereafter, when the rotation speed N reaches the rotation speed N21slightly lower than the rotation speed N2 (rated heating condition), theline voltage reaches the inverter maximum output voltage, and thefield-weakening control is started. Although the copper loss increasesas a result of start of the field-weakening control, high motorefficiency can be obtained since the bus voltage has been increased bythe converter 102.

That is, as indicated by the solid line in FIG. 28, high motorefficiency can be obtained at both of the rotation speed N1(intermediate heating condition) and the rotation speed N2 (ratedheating condition).

Next, the improving effect of the motor torque will be described. FIG.29 is a graph showing relationships between the motor torque and therotation speed in the case where the connection state of the coils 3 isthe Y connection and the case where the connection state of the coils 3is the delta connection. The motor torque (solid line) in the case ofthe Y connection is similar to that in FIG. 18. When the field-weakeningcontrol is started at the rotation speed N21 slightly lower than therotation speed N2 (rated heating condition), the motor torque (chainline) in the case of the delta connection decreases as the rotationspeed N increases.

FIG. 30 is a graph showing a relationship between the motor torque andthe rotation speed in a case where the connection state of the coils 3is the Y connection, the number of turns is adjusted such that the linevoltage reaches the inverter maximum output voltage at the rotationspeed N11, the connection state is switched from the Y connection to thedelta connection at the rotation speed NO (>N1), and the bus voltage isfurther raised. As shown in FIG. 30, when the field-weakening control isstarted at the rotation speed N11 slightly lower than the rotation speedN1 (intermediate heating condition), the motor torque decreases as therotation speed N increases.

When the rotation speed N further increases to reach the rotation speedNO, the connection state of the coils 3 is switched from the Yconnection to the delta connection, and the bus voltage is raised. Withthe switching to the delta connection and the raising of the busvoltage, the line voltage becomes lower than the inverter maximum outputvoltage, and thus the field-weakening control is stopped. Accordingly,the motor torque increases. Thereafter, when the field-weakening controlis started at the rotation speed N21 slightly lower than the rotationspeed N2 (rated heating condition), the motor torque decreases as therotation speed N increases.

In this manner, since the field-weakening control is not performed untilthe rotation speed N reaches the rotation speed N21 (rotation speedslightly lower than the rotation speed N2) after the switching to thedelta connection, a decrease in motor torque can be suppressedespecially in a rotation speed range including the rotation speed N2(rated heating condition).

Specifically, as indicated by the solid line in FIG. 30, high motortorque can be obtained at both of the rotation speed N1 (intermediateheating condition) and the rotation speed N2 (rated heating condition).That is, high performance (motor efficiency and motor torque) can beobtained in both of the intermediate heating condition and the ratedheating condition of the air conditioner 5.

In this regard, when the voltage of the converter 102 is raised, a lossdue to the raising of the voltage occurs. Thus, in the connection stateunder the intermediate heating condition (i.e., Y connection) where acontribution ratio to the motor efficiency is the highest, it ispreferable to use the power supply voltage without raising. The powersupply voltage of the power source 101 is 200 V (effective value), andthe maximum value is 280 V (=200V×√2). Accordingly, it can be said thatthe bus voltage (280 V) of the converter 102 in the case of the Yconnection is the same as the maximum value of the power supply voltage.

Further, switching of the bus voltage supplied to the inverter 103 maybe performed by raising or lowering the power supply voltage.

Further, in the operation control of the air conditioner 5 describedabove, the Y connection is set to the rotation speed N1 (intermediateheating condition) and the delta connection is set to the rotation speedN2 (rated heating condition). However, if no specific load condition isdetermined, the voltage level may be adjusted by setting the rotationspeed N1 as the maximum rotation speed during the operation in the Yconnection state and setting the rotation speed N2 as the maximumrotation speed during the operation in the delta connection state. Withsuch control, the efficiency of the motor 1 can be enhanced.

As described above, in the household air conditioner 5, the efficiencyof the motor 1 can be enhanced by setting the rotation speed N1 at therotation speed in the intermediate heating condition and the rotationspeed N2 at the rotation speed in the rated heating condition.

(Advantages of First Embodiment)

As described above, in the first embodiment, since the converter 102changes a level of the bus voltage in accordance with switching of theconnection state of the coils 3 by the connection switching unit 60,high motor efficiency and high motor torque can be obtained before andafter the switching of the connection state.

Further, since the connection state of the coils 3 is switched betweenthe Y connection (first connection state) and the delta connection(second connection state) in which the line voltage is lower than in thefirst connection state, the connection state suitable for the operationstate of the motor 1 can be selected.

Further, in the first embodiment, the bus voltage of the converter 102is set to the first bus voltage V1 when the connection state of thecoils 3 is the first connection state, and the bus voltage of theconverter 102 is set to the second bus voltage V2 higher than the firstbus voltage V1 when the connection state of the coils 3 is the secondconnection state. Thus, when the rotation speed of the motor 1increases, the connection state is switched to the second connectionstate in which the line voltage is low, and the bus voltage isincreased, so that motor efficiency and motor torque can be enhanced.

Further, in the case where the first connection state is the Yconnection, the second connection state is the delta connection, and thefirst rotation speed N1 and the second rotation speed N2 of the motor 1satisfy N2/N2>√3, the connection state of the coils 3 is set to the Yconnection when the rotation speed of the motor 1 is the first rotationspeed N1, and the connection state of the coils 3 is set to the deltaconnection when the rotation speed of the motor 1 is the second rotationspeed N2. Thus, motor efficiency and motor torque can be enhanced atboth of the rotation speeds N1 and N2.

Further, the first bus voltage V1, the second bus voltage V2, the firstrotation speed N1 and the second rotation speed N2 satisfyV2≥(V1/√3)×N2/N1, and thus high motor efficiency and high motor torquecan be obtained at the rotation speeds N1 and N2.

Further, since the first rotation speed N1 corresponds to theintermediate heating condition, and the second rotation speed N2corresponds to the rated heating condition, high motor efficiency andhigh motor torque can be obtained at the intermediate heating conditionand the rated heating condition for which performance is to be improved.

That is, since the first rotation speed N1 corresponds to a conditionthat yields the highest ratio in the annual performance factor (APF),and the second rotation speed N2 corresponds to a condition that yieldsthe second highest ratio in the annual performance factor, a largeenhancing effect of energy consumption efficiency is obtained.

Further, since the first bus voltage V1 is the same as √2 times aneffective value of the power supply voltage, the converter 102 can usethe power supply voltage without raising it when the coils 3 is in thefirst connection state, and thus energy efficiency can be enhanced.

Further, since the converter 102 is composed of a SiC element or a GaNelement, loss due to an increase in voltage is small, and thus energyefficiency can be further enhanced.

Further, since the field-weakening control is performed in accordancewith the rotation speed of the motor 1 in each of the cases of the Yconnection (first connection state) and the delta connection (secondconnection state), the rotation speed of the motor 1 can be increasedeven when the line voltage reaches the inverter maximum output voltage.

Further, in a case where the controller 50 receives the operation stopsignal from the remote controller 55 through the signal receiving unit56, the connection state of the coils 3 is switched from the Yconnection to the delta connection, and then the controller 50terminates the operation of the air conditioner 5. In a case where theconnection state of the coils 3 is already the delta connection, thisconnection state is unchanged. Accordingly, at the start of theoperation (start-up) of the air conditioner 5, the operation of the airconditioner 5 can be started in a state where the connection state ofthe coils 3 is the delta connection. Accordingly, even in a case wherethe temperature difference ΔT between the room temperature Ta and theset temperature Ts is large, the operation of the air conditioner 5 canbe started in the delta connection state, and the room temperature Tacan be quickly brought close to the set temperature Ts.

First Modification

Next, a first modification of the first embodiment will be described. Inthe first embodiment described above, the rotation speed NO at which theconnection state of the coils is switched from the Y connection to thedelta connection (i.e., the rotation speed when the temperaturedifference ΔT becomes equal to the threshold ΔTr) is equal to therotation speed NO (temperature difference) at which the connection stateis switched from the delta connection to the Y connection, but theserotation speeds may be different from each other.

FIGS. 31(A) and 31(B) are graphs each showing a relationship between themotor efficiency and the rotation speed in a case where the connectionstate is switched by the connection switching unit 60 and the busvoltage is switched by the converter 102. As shown in FIGS. 31(A) and31(B), a rotation speed N4 at which the connection state of the coils 3is switched from the Y connection to the delta connection and a rotationspeed N5 at which the connection state of the coils 3 is switched fromthe delta connection to the Y connection are different from each other.

Further, switching of the bus voltage by the converter 102 is performedat the same time as switching of the connection state of the coils 3.That is, the bus voltage is raised when the rotation speed is N4 atwhich the Y connection is switched to the delta connection. Meanwhile,the bus voltage is lowered when the rotation speed is N5 at which thedelta connection is switched to the Y connection.

Such control can be performed by, for example, setting the threshold ΔTrin step S107 and the threshold ΔTr in step S108 in FIG. 10 to differentvalues. In the examples shown in FIGS. 31(A) and 31(B), the rotationspeed N4 at which the Y connection is switched to the delta connectionis higher than the rotation speed N5 at which the delta connection isswitched to the Y connection, but this relationship may be reversed. Theother operations and configurations in the first modification aresimilar to those in the first embodiment.

In this first modification, the connection state of the coils 3 isswitched based on the room temperature Ta, and thus the operation stateof the compressor 41 can quickly respond to a rapid load change of theair conditioner 5. In addition, high motor efficiency can be obtained byswitching the bus voltage of the converter 102 in accordance with theswitching of the connection state of the coils 3.

Second Modification

Next, a second modification of the first embodiment will be described.In the first embodiment described above, the bus voltage of theconverter 102 is switched to two stages (V1/V2), but the bus voltage maybe switched to three stages as shown in FIG. 32.

FIG. 32 is a graph showing a relationship between a line voltage and arotation speed in a case where switching of the connection state andswitching of the bus voltage of the converter 102 are performed in thesecond modification. In the example of FIG. 32, the bus voltage of theconverter 102 is set to V1 when the rotation speed is N1 (Y connection)corresponding to the intermediate heating condition, and the connectionstate is switched from the Y connection to the delta connection when therotation speed is N6 between the rotation speed N1 and the rotationspeed N2 (rated heating condition), and the bus voltage is raised to V2at the same as the switching of the connection state.

In addition, when the rotation speed is N7 higher than the rotationspeed N2, the bus voltage of the converter 102 is raised to V3 while theconnection state is unchanged. During a period from the rotation speedN7 to a maximum rotation speed N8, the bus voltage of the converter 102is V3. The other operations and configurations in the secondmodification are similar to those in the first embodiment.

As described above, in the second modification, since the bus voltage ofthe converter 102 is switched to three stages of V1, V2, and V3, highmotor efficiency and high motor torque can be obtained especially in ahigh rotation speed range.

In this regard, the switching of the bus voltage is not limited to thetwo stages or the three stages, and may be performed in four or morestages. Further, in the first modification (FIG. 31), the bus voltage ofthe converter 102 may be switched to three or more stages.

Third Modification

Next, a third modification of the first embodiment will be described. Inthe first embodiment described above, the connection state of the coils3 is switched between the Y connection and the delta connection.However, the connection state of the coils 3 may be switched between aseries connection and a parallel connection.

FIGS. 33(A) and 33(B) are schematic diagrams for describing switching ofthe connection state of the coils 3 according to the third modification.In FIG. 33(A), the three-phase coils 3U, 3V, and 3W are connected in theY connection. Further, the coil portions Ua, Ub, and Uc of the coil 3Uare connected in series, the coil portions Va, Vb, and Vc of the coil 3Vare connected in series, and the coil portions Wa, Wb, and Wc of thecoil 3W are connected in series. That is, the coil portions of eachphase of the coils 3 are connected in series.

In contrast, in FIG. 33(B), the three-phase coils 3U, 3V, and 3W areconnected in the Y connection, but the coil portions Ua, Ub, and Uc ofthe coil 3U are connected in parallel, the coil portion Va, Vb, and Vcof the coil 3V are connected in parallel, and the coil portions Wa, Wb,and Wc of the coil 3W are connected in parallel. That is, the coilportions of each phase of the coils 3 are connected in parallel.Switching of the connection state of the coils 3 as shown in FIGS. 33(A)and 33(B) can be achieved by, for example, providing each of the coilportions of the coils 3U, 3V, and 3W with a selector switch.

Suppose that the number of coil portions (i.e., the number of rows)connected in parallel in each phase is n, the line voltage decreases to1/n times by switching from the series connection (FIG. 33(A)) to theparallel connection (FIG. 33(B)). Thus, by switching the connectionstate of the coils 3 from the series connection to the parallelconnection when the line voltage approaches the inverter maximum outputvoltage, the degree of field-weakening can be reduced (i.e., weakeningcurrent can be reduced).

In a case where there are two load conditions for which performance isto be improved and the rotation speed N1 at the low-speed side and therotation speed N2 at the high-speed side satisfy (N2/N1)>n, the linevoltage becomes larger than the inverter maximum output voltage only byswitching the connection state of the coils 3 from the series connectionto the parallel connection, and thus the field-weakening control isnecessary. Thus, as described in the first embodiment, the bus voltageof the converter 102 is raised at the same time as when the connectionstate of the coils 3 is switched from the series connection to theparallel connection. Accordingly, high motor efficiency and high motortorque can be obtained in both of the rotation speed range including therotation speed N1 and the rotation speed range including the rotationspeed N2.

FIGS. 34(A) and 34(B) are schematic diagrams for describing anotherconfiguration example of the third modification. In FIG. 34(A), thethree-phase coils 3U, 3V, and 3W are connected in the delta connection.Further, the coil portions Ua, Ub, and Uc of the coil 3U are connectedin series, the coil portions Va, Vb, and Vc of the coil 3V are connectedin series, and the coil portions Wa, Wb, and Wc of the coil 3W areconnected in series. That is, the coil portions of each phase of thecoils 3 are connected in series.

In contrast, in FIG. 34(B), the three-phase coils 3U, 3V, and 3W areconnected in the delta connection, but the coil portions Ua, Ub, and Ucof the coil 3U are connected in parallel, the coil portion Va, Vb, andVc of the coil 3V are connected in parallel, and the coil portions Wa,Wb, and Wc of the coil 3W are connected in parallel. That is, the coilportions of each phase of the coils 3 are connected in parallel.

In this case, similarly to the examples shown in FIGS. 33(A) and 33(B),when the low-speed side rotation speed N1 and the high-speed siderotation speed N2 of the two load conditions for which performance is tobe improved satisfy (N2/N1)>n, the connection state of the coils 3 isswitched from the series connection (FIG. 33(A)) to the parallelconnection (FIG. 33(B)), and at the same time, the bus voltage of theconverter 102 is raised. The other operations and configurations in thethird modification are similar to those in the first embodiment. It issufficient that the raised bus voltage V2 satisfies V2 (V1/n)×N2/N1 inrelation to the bus voltage V1 before raising.

As described above, in the third modification, the connection state ofthe converter 102 is switched between the series connection and theparallel connection, and therefore the degree of field-weakening can bereduced and the motor efficiency can be increased. Further, the busvoltages V1 and V2 and the rotation speeds N1 and N2 satisfy V2(V1/n)×N2/N1, and therefore high motor efficiency and high motor torquecan be obtained at the rotation speeds N1 and N2.

In the first and second modifications, switching between the seriesconnection (first connection state) and the parallel connection (secondconnection state) may be performed.

Fourth Modification

In the first embodiment described above, the absolute value of thedifference ΔT between the room temperature Ta detected by the roomtemperature sensor 54 and the set temperature Ts is compared to thethreshold ΔTr, and the connection state of the coils 3 and the busvoltage of the converter 102 are switched. However, an air-conditioningload may be calculated based on the room temperature Ta, and theconnection state of the coils 3 and the bus voltage of the converter 102may be switched based on the air-conditioning load.

FIG. 35 is a flowchart showing a basic operation of an air conditioneraccording to a fourth modification. Steps S101 through S105 are the sameas those in the first embodiment. If the operation stop signal is notreceived after the motor 1 is started in step S104 (step S105), thecontroller 50 acquires a temperature difference ΔT between a roomtemperature Ta detected by the room temperature sensor 54 and a settemperature Ts set by the remote controller 55 (step S201), andcalculates an air-conditioning load based on the temperature differenceΔT (step S202).

Next, based on the calculated air-conditioning load, it is determinedwhether switching of the coils 3 from the delta connection to the Yconnection is necessary or not. Specifically, it is determined whetheror not the connection state of the coils 3 is the delta connection andthe air-conditioning load calculated in step S202 is less than or equalto a threshold (reference value of the air-conditioning load) (stepS203).

If the result of the comparison in step S203 indicates that theconnection state of the coils 3 is the delta connection and theair-conditioning load is less than or equal to the threshold, processesin steps S121 through S124 shown in FIG. 11 are performed. As describedin the first embodiment, in steps S121 through S124 in FIG. 11, theswitching from the delta connection to the Y connection and the raisingof the bus voltage by the converter 102 are performed.

If the result of the comparison in step S203 indicates that theconnection state of the coils 3 is not the delta connection (if it isthe Y connection) or that the air-conditioning load is larger than thethreshold (i.e., if switching to the Y connection is unnecessary), theprocess proceeds to step S204.

In step S204, it is determined whether switching from the Y connectionto the delta connection is necessary or not. Specifically, it isdetermined whether or not the connection state of the coils 3 is the Yconnection and the air-conditioning load calculated in step S202 islarger than the threshold.

If the result of the comparison in step S204 indicates that theconnection state of the coils 3 is the Y connection and theair-conditioning load is larger than the threshold, processes in stepsS131 through S134 shown in FIG. 12 are performed. As described in thefirst embodiment, in steps S131 through S134 in FIG. 12, the switchingfrom the Y connection to the delta connection and the lowering of thebus voltage by the converter 102 are performed.

If the result of the comparison in step S204 indicates that theconnection state of the coils 3 is not the Y connection (if it is thedelta connection) or that the air-conditioning load is larger than thethreshold (i.e., if switching to the delta connection is unnecessary),the process returns to step S105. Processes in the case where theoperation stop signal is received (steps S109 through S111) are similarto those in the first embodiment. The other operations andconfigurations in the fourth modification are similar to those in thefirst embodiment.

As described above, in the fourth modification, the air-conditioningload is calculated based on the room temperature Ta and the connectionstate of the coils 3 and the bus voltage of the converter 102 areswitched based on the calculated air-conditioning load, and thereforethe operation state of the compressor 41 can quickly respond to a loadchange of the air conditioner 5. As a result, comfort can be enhanced.

In the first, second, and third modifications, the connection state ofthe coils 3 and the bus voltage of the converter 102 may be switchedbased on the air-conditioning load.

Fifth Modification

In the first embodiment described above, the connection state of thecoils 3 and the bus voltage of the converter 102 are switched based onthe temperature difference ΔT between the room temperature Ta detectedby the room temperature sensor 54 and the set temperature Ts. However,the connection state of the coils 3 and the bus voltage of the converter102 may be switched based on the rotation speed of the motor 1.

FIG. 36 is a flowchart showing a basic operation of an air conditioneraccording to a fifth modification. Steps S101 through S105 are the sameas those in the first embodiment. If the operation stop signal is notreceived after the motor 1 is started in step S104 (step S105), thecontroller 50 acquires a rotation speed of the motor 1 (step S301). Therotation speed of the motor 1 is a frequency of an output current of theinverter 103, and can be detected by using a current sensor or the likemounted on the motor 1.

Next, it is determined whether switching of the coils 3 from the deltaconnection to the Y connection is necessary or not, based on thisrotation speed of the motor 1. That is, it is determined whether or notthe connection state of the coils 3 is the delta connection and therotation speed of the motor 1 is less than or equal to a threshold(reference value of the rotation speed) (step S302).

In the case of the heating operation, the threshold used in step S302 ispreferably a value (more preferably an intermediate value) between therotation speed N1 corresponding to the intermediate heating conditionand the rotation speed N2 corresponding to the rated heating condition.In the case of the cooling operation, the threshold used in step S302 ispreferably a value (more preferably an intermediate value) between therotation speed N1 corresponding to the intermediate cooling conditionand the rotation speed N2 corresponding to the rated cooling condition.

For example, in the case of the household air conditioner having arefrigeration capacity of 6.3 kW, the rotation speed N1 corresponding tothe intermediate heating condition is 35 rps and the rotation speed N2corresponding to the rated heating condition is 85 rps, and thereforethe threshold used in step S302 is preferably 60 rps, which is anintermediate value between the rotation speed N1 and the rotation speedN2.

However, the rotation speed of the motor 1 may fluctuate. Thus, in thisstep S302, it is determined whether or not a state where the rotationspeed of the motor 1 is greater than or equal to the threshold continuesfor a preset time.

If the result of the comparison in step S302 indicates that theconnection state of the coils 3 is the delta connection and the rotationspeed of the motor 1 is less than or equal to the threshold, processesin steps S121 through S124 shown in FIG. 11 are performed. As describedin the first embodiment, in steps S121 through S124 in FIG. 11, theswitching from the delta connection to the Y connection and the raisingof the bus voltage of the converter 102 are performed.

If the result of the comparison in step S302 indicates that that theconnection state of the coils 3 is not the delta connection (if it is,is the Y connection) or that the rotation speed of the motor 1 isgreater than the threshold (i.e., switching to the Y connection isunnecessary), the process proceeds to step S303.

In step S303, it is determined whether switching from the Y connectionto the delta connection is necessary or not. Specifically, it isdetermined whether or not the connection state of the coils 3 is the Yconnection and the rotation speed of the motor 1 is greater than thethreshold.

If the result of the comparison in step S303 indicates that theconnection state of the coils 3 is the Y connection and the rotationspeed of the motor 1 is greater than the threshold, processes in stepsS131 through S134 shown in FIG. 12 are performed. As described in thefirst embodiment, in steps S131 through S134 in FIG. 12, the switchingfrom the Y connection to the delta connection and the lowering of thebus voltage of the converter 102 are performed.

If the result of the comparison in step S303 indicates that theconnection state of the coils 3 is not the Y connection (if it is thedelta connection) or that the rotation speed of the motor 1 is greaterthan the threshold (i.e., if switching to the delta connection isunnecessary), the process returns to step S105. Processes in the casewhere the operation stop signal is received (steps S109 through S111)are similar to those in the first embodiment. The other operations andconfigurations in the fifth modification are similar to those in thefirst embodiment.

As described above, in the fifth modification, the connection state ofthe coils 3 and the bus voltage of the converter 102 are switched basedon the rotation speed of the motor 1, and therefore high motorefficiency and high motor torque can be obtained.

In this regard, the connection state of the coils 3 and the bus voltageof the converter 102 may be switched based on the rotation speed of themotor 1 in the first, second, and third modifications.

In this regard, although the rotary compressor 8 has been described asan example of the compressor, the motor of the embodiment may be appliedto a compressor other than the rotary compressor 8.

Second Embodiment

Next, a second embodiment of the present invention will be described.

(Configuration of Air Conditioner)

FIG. 37 is a block diagram illustrating a configuration of an airconditioner 500 according to the second embodiment. FIG. 38 is a blockdiagram illustrating a control system of the air conditioner 500according to the second embodiment. FIG. 39 is a block diagramillustrating a control system of a driving device 100 a according to thesecond embodiment. The air conditioner 500 according to the secondembodiment further includes a compressor temperature sensor 71 as acompressor state detection unit. The compressor temperature sensor 71 isa temperature sensor for detecting a compressor temperature T_(C)indicating a state of the rotary compressor 8. In this regard, thecompressor state detection unit may be a detector capable of detectingthe state of the rotary compressor 8, and is not limited to thetemperature sensor.

Except for the compressor temperature sensor 71, configurations of theair conditioner 500 and the driving device 100 a according to the secondembodiment are the same as those of the air conditioner 5 and thedriving device 100 according to the first embodiment, respectively.

In the example illustrated in FIG. 39, the driving device 100 a includesa converter 102 for rectifying an output of a power source 101, aninverter 103 for outputting an AC voltage to coils 3 of a motor 1, aconnection switching unit 60 for switching the connection state of thecoils 3, a controller 50, and the compressor temperature sensor 71. Theconverter 102 is supplied with electric power from the power source 101as an alternating current (AC) power source.

The configuration of the driving device 100 a according to the secondembodiment is similar to that of the driving device 100 according to thefirst embodiment, except for the compressor temperature sensor 71. Inthis regard, the compressor temperature sensor 71 may not be a componentof the driving device 100 a. The driving device 100 a is used togetherwith the rotary compressor 8, and drives the motor 1.

A neodymium rare earth magnet containing neodymium-iron-boron (Nd—Fe—B)as a main component is used in a permanent magnet type motor, and hascharacteristics such that a coercive force decreases with temperature.When the motor using a neodymium rare earth magnet is used in ahigh-temperature atmosphere of 140° C. as in a compressor, the coerciveforce of the magnet decreases with temperature (−0.5 to −0.6%/ΔK), andtherefore it is necessary to add a dysprosium (Dy) element to enhancethe coercive force.

When the Dy element is added to the magnet, the coercive force isenhanced, but there is a disadvantage such that a residual flux densitydecreases. When the residual flux density decreases, a magnet torque ofthe motor decreases and a supply current increases, and accordingly acopper loss increases. Thus, there is a strong demand for reducing anadding amount of Dy in terms of efficiency.

For example, when the maximum temperature of the compressor while thecompressor is driven is reduced, the maximum temperature of the magnetscan be reduced, and demagnetization of the magnets can be alleviated.Thus, it is effective to control the compressor (for example, therotation speed of the motor) based on a compressor temperature thresholdas a threshold for limiting the temperature of the compressor.

However, if the compressor temperature threshold is set to be low, aninstruction to reduce the rotation speed of the motor or an instructionto stop the motor may be issued in a state where the load(air-conditioning load) is low, depending on the set value. In thiscase, the maximum operation range of the motor is narrowed, andoperation of the motor is restricted irrespective of the situation inthe room (for example, the temperature difference ΔT described above) inwhich the air conditioner is provided.

Thus, in the second embodiment, the controller 50 issues an instructionto change a method for driving the motor 1 based on different thresholds(compressor temperature thresholds) depending on the connection state ofthe coils 3. Specifically, if it is determined that the compressortemperature T_(C) detected by the compressor temperature sensor 71 ishigher than the compressor temperature threshold, the controller 50issues an instruction to change the driving method of the motor 1.Accordingly, the temperature of the rotary compressor 8 is reduced, andthe rotary compressor 8 is protected.

The compressor temperature sensor 71 detects a compressor temperatureT_(C) indicating the state of the rotary compressor 8. In thisembodiment, the compressor temperature sensor 71 is fixed to a dischargepipe 85 of the rotary compressor 8. However, the position to which thecompressor temperature sensor 71 is fixed is not limited to thedischarge pipe 85.

The compressor temperature T_(C) is a temperature of at least one of ashell 80 of the rotary compressor 8, the discharge pipe 85 (for example,an upper portion of the discharge pipe 85) of the rotary compressor 8,refrigerant in the rotary compressor 8 (for example, refrigerant flowingin the discharge pipe 85), and the motor 1 disposed in the rotarycompressor 8. The compressor temperature T_(C) may be a temperature ofan element other than these elements.

The compressor temperature T_(C) is, for example, a maximum temperaturemeasured within a preset time period. A correlation between temperaturedata in the rotary compressor 8 measured in advance and the compressortemperature T_(C) may be stored in a memory in the controller 50 foreach measurement target of the compressor temperature T_(C). Thetemperature data in the rotary compressor 8 measured in advance is dataindicating a temperature (maximum temperature) in the rotary compressor8 that varies depending on a circulation amount of refrigerant, a heatgeneration temperature of the motor 1, and the like. In this case, thecompressor temperature T_(C) detected by the compressor temperaturesensor 71 may be used as a first detection value or a second detectionvalue described later. The temperature data calculated based on thecorrelation with the compressor temperature T_(C) may be used as a firstdetection value or a second detection value described later.

When the connection state of the coils 3 is the first connection state(for example, the Y connection), the controller 50 controls the motor 1based on the first detection value detected by the compressortemperature sensor 71 and a threshold T_(Y) (first threshold) as thecompressor temperature threshold. The threshold T_(Y) is, for example,90° C. In the case where a detector other than the temperature sensor isused as the compressor state detection unit, a value other than thetemperature may be set as the threshold.

Specifically, if the first detection value is larger than the thresholdT_(Y), the controller 50 controls the motor 1 such that at least onetemperature detected by the compressor temperature sensor 71 (compressortemperature T_(C)) decreases. For example, the controller 50 issues aninstruction to change the rotation speed of the motor 1 to therebyreduce the rotation speed of the motor 1, or stops driving (rotation) ofthe motor 1. Accordingly, the compressor temperature T_(C) can bereduced.

When the connection state of the coils 3 is the second connection state(for example, the delta connection), the controller 50 controls themotor 1 based on the second detection value detected by the compressortemperature sensor 71 and a threshold T_(Δ) (second threshold) as thecompressor temperature threshold.

Specifically, if the second detection value is larger than the thresholdT_(Δ), the controller 50 controls the motor 1 such that at least onetemperature detected by the compressor temperature sensor 71 (compressortemperature T_(C)) decreases. For example, the controller 50 issues aninstruction to change the rotation speed of the motor 1 to therebyreduce the rotation speed of the motor 1, or stops driving (rotation) ofthe motor 1. Accordingly, the compressor temperature T_(C) can bereduced.

The motor 1 is designed so that the magnets are not demagnetized at themaximum temperature (compressor temperature threshold) the magnets canreach, taking into consideration a temperature change due to heatgeneration of the motor 1, a cooling effect by refrigerant, and thelike. For example, in this embodiment, the permanent magnets 25 of themotor 1 are designed so that the magnets are not demagnetized at near140° C., which is the maximum magnet temperature. In this case, thethreshold TA is set to 140° C.

The compressor temperature threshold is set to be higher in theconnection state in which the line voltage is lower, out of theconnection states of the coils 3 switchable by the connection switchingunit 60. In this embodiment, the line voltage of the inverter 103 in thedelta connection is lower than the line voltage of the inverter 103 inthe Y connection. Thus, the threshold T_(Δ) is set to be larger than thethreshold T_(Y). Accordingly, it is possible to prevent the maximumoperation range of the motor 1 (especially the maximum rotation speed ofthe motor 1 in the delta connection) from being narrowed.

(Operation of Air Conditioner)

Next, a basic operation of the air conditioner 500 according to thesecond embodiment (method for controlling the motor 1, the rotarycompressor 8, and the air conditioner 500) will be described.

FIG. 40 is a flowchart showing a basic operation of the air conditioner500 according to the second embodiment.

Steps S101 through S105 are similar to those in the first embodiment(FIG. 10). In a case where the operation stop signal is not received instep S105, the process proceeds to step S401.

In accordance with the temperature difference ΔT, the rotation speed ofthe motor 1 or the like, the connection switching unit 60 switches theconnection state of the coils 3 between the delta connection (secondconnection state in this embodiment) and the Y connection (firstconnection state in this embodiment).

The compressor temperature sensor 71 detects the state of the rotarycompressor 8 (step S401). In this embodiment, the compressor temperaturesensor 71 detects the compressor temperature T_(C) (for example, thetemperature of the discharge pipe 85) indicating the state of the rotarycompressor 8.

In step S401, when the connection state of the coils 3 is the Yconnection, the compressor temperature T_(C) is detected as a firstdetection value. In contrast, when the connection state of the coils 3is the delta connection, the compressor temperature T_(C) is detected asa second detection value.

Further, the controller 50 determines whether or not the connectionstate of the coils 3 is the Y connection and the compressor temperatureT_(C) is greater than the threshold T_(Y) (step S402).

If the result of the comparison in S402 indicates that the connectionstate of the coils 3 is the Y connection and the compressor temperatureT_(C) is greater than the threshold T_(Y), the process proceeds to stepS404.

If the result of the comparison in step S402 indicates that theconnection state of the coils 3 is not the Y connection (if it is thedelta connection), or that the compressor temperature T_(C) is less thanor equal to the threshold T_(Y), the process returns to step S403.

In step S403, the controller 50 determines whether or not the connectionstate of the coils 3 is the delta connection and the compressortemperature T_(C) is greater than the threshold T_(Δ).

If the result of the comparison in S403 indicates that the connectionstate of the coils 3 is the delta connection and the compressortemperature T_(C) is greater than the threshold T_(Δ), the processproceeds to step S404.

If the result of the comparison in step S403 indicates that theconnection state of the coils 3 is not the delta connection (if it isthe Y connection), or that the compressor temperature T_(C) is less thanor equal to the threshold T_(Δ), the process returns to step S105.

In step S404, the controller 50 reduces the rotation speed of the motor1. In this regard, instead of reducing the rotation speed of the motor1, the motor 1 may be stopped. In the case where the motor 1 is stoppedin step S404, the motor 1 is stopped without changing the connectionstate of the coils 3. In the case where the motor 1 is stopped in stepS404, the motor 1 is started after a lapse of a preset time and then theprocess returns to step S105, for example.

That is, in steps S401 through S404, when the connection state of thecoils 3 is the Y connection, the motor 1 is controlled based on thefirst detection value and the first threshold (threshold T_(Y)), whereaswhen the connection state of the coils 3 is the delta connection, themotor 1 is controlled based on the second detection value and the secondthreshold (threshold T_(Δ)). Accordingly, the rotary compressor 8 can becontrolled such that the compressor temperature T_(C) is lower than thethreshold T_(Y) or the threshold T_(Δ).

If the operation stop signal is received in step S105 described above,the controller 50 stops rotation of the motor 1 (step S109). In thisregard, if the operation stop signal is received in a state where themotor 1 is stopped in step S404, the process proceeds to step S110 whilethe motor 1 is stopped. In this regard, although not shown in FIG. 40,if the operation stop signal is received during a period between stepsS401 through S404, the process proceeds to step S109 and rotation of themotor 1 is stopped.

Thereafter, the controller 50 performs a process of stopping the airconditioner 500 (step S110). Specifically, the fan motors of the indoorfan 47 and the outdoor fan 46 are stopped. Thereafter, the CPU 57 of thecontroller 50 is stopped, and operation of the air conditioner 500 isterminated.

In the case where the process of stopping the air conditioner 500 isperformed in step S110, the connection state of the coils 3 ispreferably the delta connection. For example, in step S110, if theconnection state of the coils 3 is the Y connection, the controller 50outputs the connection switching signal to the connection switching unit60 to switch the connection state of the coils 3 from the Y connectionto the delta connection.

(Advantages of Second Embodiment)

According to the second embodiment, the motor 1 is controlled by usingthe compressor temperature threshold in consideration of the connectionstate of the coils 3. For example, if the detected value detected by thecompressor temperature sensor 71 is greater than the compressortemperature threshold, the motor 1 is controlled such that thecompressor temperature T_(C) (i.e., the temperature in the rotarycompressor 8) decreases. As a result, demagnetization in the motor 1 canbe prevented, and the motor 1 can be appropriately controlled inaccordance with the state of the rotary compressor 8.

As described in the first embodiment, in the driving device thatoperates while switching the connection state of the coils 3 between theY connection and the delta connection, a conventional high-speedoperation is performed with the delta connection, whereas a low-speedoperation for a small air-conditioning load is performed with the Yconnection. Thus, by switching the connection state of the coils 3 fromthe delta connection to the Y connection, the maximum temperature of therotary compressor 8 (the maximum value of the compressor temperatureT_(C)) in performing a normal load operation can be set in such a mannerthat the maximum temperature of the rotary compressor 8 during theoperation in the Y connection state is lower than that during theoperation in the delta connection state.

For example, in a case where the motor 1 is controlled based on onepreset compressor temperature threshold (for example, the same value asthe threshold T_(Y)) without taking the connection state of the coil 3into consideration, there is a case where the maximum operating range ofthe motor 1 (especially, the maximum rotation speed of the motor 1 inthe delta connection state) may be narrowed. Thus, in the secondembodiment, the motor 1 is controlled by using a plurality of compressortemperature thresholds by taking the connection state of the coils 3into consideration.

Specifically, the motor 1 is controlled based on different compressortemperature thresholds (for example, threshold T_(Y) and thresholdT_(Δ)) depending on the connection states of the coils 3. Thus, even ifthe compressor temperature threshold is set lower during the operationin the Y connection state than during the operation in the deltaconnection state, the maximum operation range of the motor 1(especially, the maximum rotation speed of the motor 1 in the deltaconnection) can be prevented from being narrowed.

For example, in the configuration in which the connection state of thecoils 3 is switched as described in the first embodiment, when theconnection state of the coils 3 is the Y connection and the rotationspeed of the motor 1 is low (intermediate heating condition), the linevoltage (motor voltage) is approximately equal to the inverter maximumoutput voltage, so that the efficiency is improved. In this case, thereis a case where it is desired to rotate the motor 1 at a rotation speedas high as possible in order to reduce the number of times of connectionswitching. For this reason, operation is performed usingfield-weakening. However, the weakening current increases, anddemagnetization deteriorates.

As the temperature is lower, the coercive force of the permanent magnet25 is higher and the permanent magnet 25 is less likely to bedemagnetized even when the current is increased. Thus, according to thesecond embodiment, the compressor temperature threshold T_(Y) when theconnection state of the coils 3 is the Y connection is set to be lowerthan the compressor temperature threshold T_(Δ) in the delta connection.Thus, the maximum temperature of the rotary compressor 8 during theoperation in the Y connection state can be lower than that during theoperation in the delta connection state. Accordingly, a configuration inwhich demagnetization does not occur even when the weakening currentincreases is achieved, and it becomes possible to perform driving in theY connection state at a higher rotation speed. Thus, there is anadvantage such that flexibility in switching the connection can beincreased. In other words, the motor 1 can be driven in a state wherethe coercive force of the magnets of the motor 1 is high, anddemagnetization is less likely to occur even when a larger current flowsin the motor 1. Furthermore, when the connection state of the coils 3 isthe Y connection, the motor 1 can be driven at a higher rotation speedusing field-weakening.

Further, in the case where the connection of the coils is switched tothe delta connection from the Y connection in which the winding number(number of turns) is close to the number of turns of conventional coilsthat are not subjected to connection switching, field-weakening at ahigh rotation speed can be suppressed, and a configuration resistant todemagnetization in the delta connection as compared to a conventionalconfiguration can be obtained.

Furthermore, in the Y connection, since the compressor temperaturethreshold can be set lower than that of the conventional configuration,demagnetization characteristics can be enhanced in both of the Yconnection and the delta connection, and the magnet to which nodysprosium (Dy) is added can be used.

For example, as the permanent magnet 25, a rare earth magnet containingneodymium (Nd), iron (Fe), and boron (B) as main components can be used,and this permanent magnet 25 does not contain dysprosium (Dy) as anadditive for increasing the coercive force. In this case, the permanentmagnet 25 has the residual magnetic flux density of 1.36 T to 1.42 T,the coercive force of 1671 kA/m to 1989 kA/m, and the maximum energyproduct of 354 kJ/m³ to 398 kJ/m³.

Modification of Second Embodiment

Next, a modification of the second embodiment of the present inventionwill be described. The second embodiment can be combined with the firstembodiment (including the modifications thereof). Thus, in themodification of the second embodiment, another example of operation ofthe air conditioner described in the second embodiment (method forcontrolling the motor 1, the rotary compressor 8, and the airconditioner 500) will be described. A configuration of an airconditioner according to the modification of the second embodiment isthe same as that of the air conditioner 500 of the second embodiment.Thus, the air conditioner of the modification of the second embodimentwill be referred to as the air conditioner 500.

FIG. 41 is a flowchart showing a basic operation of the air conditioner500 according to the modification of the second embodiment.

Steps S101 through S106 are similar to those in the first embodiment(FIG. 10).

In step S107, the controller 50 determines whether switching of theconnection state of the coils 3 from the delta connection to the Yconnection is necessary or not based on the temperature difference ΔTbetween the room temperature Ta detected by the room temperature sensor54 and the set temperature Ts set by the remote controller 55. That is,it is determined whether or not the connection state of the coils 3 isthe delta connection and the absolute value of the temperaturedifference ΔT is less than or equal to the threshold ΔTr (step S107).

If the result of the comparison in step S107 indicates that theconnection state of the coils 3 is the delta connection and the absolutevalue of the temperature difference ΔT is less than or equal to thethreshold ΔTr, the process proceeds to step S121 (FIG. 11).

If the result of the comparison in step S107 indicates that theconnection state of the coils 3 is not the delta connection (if it isthe Y connection), or that the absolute value of the temperaturedifference ΔT is larger than the threshold ΔTr (i.e., switching to the Yconnection is unnecessary), the process proceeds to step S108.

In step S108, it is determined whether switching from the Y connectionto the delta connection of the coils 3 is necessary or not. For example,similarly to the first embodiment (step S108), the controller 50determines whether or not the connection state of the coils 3 is the Yconnection and the absolute value of the temperature difference ΔTdescribed above is larger than the threshold ΔTr.

If the result of the comparison in step S108 indicates that theconnection state of the coils 3 is the Y connection and the absolutevalue of the temperature difference ΔT is larger than the threshold ΔTr,the process proceeds to step S131 (FIG. 12). In the modification of thesecond embodiment, the processes in steps S131 through S134 shown inFIG. 12 may be replaced by the processes (steps S135, S136, and S131through S134) shown in FIG. 13(A) or the processes (steps S137, S138,and S131 through S134) shown in FIG. 13(B).

The processes in steps S106 through S108 shown in FIG. 41 may bereplaced by the processes in the modifications of the first embodiment(e.g., steps S201 through S204 shown in FIG. 35 or steps S301 throughS303 shown in FIG. 36).

If the result of the comparison in step S108 indicates that theconnection state of the coils 3 is not the Y connection (if it is thedelta connection), or that the absolute value of the temperaturedifference ΔT is less than or equal to the threshold ΔTr (i.e., ifswitching to the delta connection is unnecessary), the process proceedsto step S401.

Steps S401 through S404 are similar to those in the second embodiment(FIG. 40).

If the operation stop signal is received in step S105 described above,the controller 50 stops rotation of the motor 1 (step S109). If theoperation stop signal is received in a state where the motor 1 stoppedin step S404, the process proceeds to step S110 in a state where themotor 1 is stopped. Although not shown in FIG. 41, if the operation stopsignal is received in the steps S105 through S108 or the steps S401through S404, the process proceeds to step S109 and rotation of themotor 1 is stopped.

Thereafter, the controller 50 (specifically, the connection switchingunit 60) switches the connection state of the coils 3 from the Yconnection to the delta connection (step S110). If the connection stateof the coils 3 is already the delta connection, the connection state isunchanged.

Step S111 is similar to that in the first embodiment (FIG. 10).

The modification of the second embodiment has the same advantages asthose described in the first embodiment (including the modificationsthereof) and the second embodiment.

Features of the embodiments and the modifications described above can becombined as appropriate.

Although the preferred embodiments of the present invention have beenspecifically described above, the present invention is not limited tothe above described embodiments, and various modifications or variationscan be made without departing from the gist of the present invention.

What is claimed is:
 1. A driving device to drive a motor having coils,the driving device comprising: a converter to generate a bus voltage; aninverter to convert the bus voltage to an AC voltage and supply the ACvoltage to the coils; and a connection switching device to switch aconnection state of the coils; wherein the connection state of the coilshas a first connection state and a second connection state; wherein aline voltage in the coils is lower in the second connection state thanin the first connection state for a same rotation speed of the motor;and wherein in a case where the connection switching device switches theconnection state of the coils from the first connection state to thesecond connection state, the bus voltage generated by the converter isswitched from a first bus voltage V1 to a second bus voltage V2 higherthan the first bus voltage V1.
 2. The driving device according to claim1, wherein in a case where the connection switching device switches theconnection state of the coils from the first connection state to thesecond connection state, rotation of the motor is stopped temporarily,and the connection switching device switches the connection state of thecoils from the first connection state to the second connection statewhile the motor is stopped.
 3. The driving device according to claim 1,wherein the coils are three-phase coils, and wherein the firstconnection state is a state where the three-phase coils are connected ina Y connection, and the second connection state is a state where thethree-phase coils are connected in a delta connection.
 4. The drivingdevice according to claim 3, wherein a first rotation speed N1 and asecond rotation speed N2 of the motor satisfy N2/N1>√3; wherein in acase where a rotation speed of the motor is the first rotation speed N1,the connection switching device sets the connection state of the coilsto the first connection state; and wherein in a case where the rotationspeed of the motor is the second rotation speed N2, the connectionswitching device sets the connection state of the coils to the secondconnection state.
 5. The driving device according to claim 4, whereinthe first bus voltage V1, the second bus voltage V2, the first rotationspeed N1 and the second rotation speed N2 satisfy V2≥(V1/√3)×N2/N1. 6.The driving device according to claim 1, wherein the coils arethree-phase coils connected in a Y connection or a delta connection,wherein the first connection state is a state where the three-phasecoils have serially-connected coil portions in a first number for eachphase, and wherein the second connection state is a state where thethree-phase coils have parallely-connected coil portions in the firstnumber for each phase.
 7. The driving device according to claim 6,wherein the first number is expressed as “n”; wherein a first rotationspeed N1 and a second rotation speed N2 of the motor satisfy N2/N1>n;wherein in a case where a rotation speed of the motor is the firstrotation speed N1, the connection switching device sets the connectionstate of the coils to the first connection state; and wherein in a casewhere the rotation speed of the motor is the second rotation speed N2,the connection switching device sets the connection state of the coilsto the second connection state.
 8. The driving device according to claim7, wherein the first bus voltage V1, the second bus voltage V2, thefirst rotation speed N1 and the second rotation speed N2 satisfyV2≥(V1/n)×N2/N1.
 9. The driving device according to claim 4, wherein themotor is used in an air conditioner; wherein the first rotation speed N1corresponds to an intermediate heating condition for the airconditioner; and wherein the second rotation speed N2 corresponds to arated heating condition for the air conditioner.
 10. The driving deviceaccording to claim 4, wherein the motor is used in an air conditioner;wherein the first rotation speed N1 corresponds to a condition thatyields a highest ratio in an annual performance factor (APF) for the airconditioner; wherein the second rotation speed N2 corresponds to acondition that yields a second highest ratio in the annual performancefactor for the air conditioner.
 11. The driving device according toclaim 1, further comprising a power source to supply an AC power supplyvoltage to the converter; wherein the first bus voltage V1 is the sameas √2 times an effective value of the power supply voltage.
 12. Thedriving device according to claim 1, wherein the connection switchingdevice switches the connection state of the motor to the firstconnection state in a case where a rotation speed of the motor is lessthan or equal to a threshold, and switches the connection state of themotor to the second connection state in a case where the rotation speedof the motor is greater than the threshold.
 13. The driving deviceaccording to claim 1, wherein the inverter performs field-weakeningcontrol in accordance with a rotation speed of the motor.
 14. Thedriving device according to claim 1, wherein the converter has a SiCelement or a GaN element.
 15. An air conditioner comprising: a motorhaving coils; a compressor driven by the motor; and a driving device todrive the motor, wherein the driving device comprises: a converter togenerate a bus voltage; an inverter to convert the bus voltage to an ACvoltage and supply the AC voltage to the coils; and a connectionswitching device to switch a connection state of the coils, wherein theconnection state of the coils has a first connection state and a secondconnection state; wherein a line voltage in the coils is lower in thesecond connection state than in the first connection state for a samerotation speed of the motor; and wherein in a case where the connectionswitching device switches the connection state of the coils from thefirst connection state to the second connection state, the bus voltagegenerated by the converter is switched from a first bus voltage V1 to asecond bus voltage V2 higher than the first bus voltage V1.
 16. A methodfor driving a motor having coils, the method using a converter togenerate a bus voltage and an inverter to convert the bus voltage to anAC voltage and supply the AC voltage to the coils, wherein theconnection state of the coils has a first connection state and a secondconnection state, and a line voltage in the coils is lower in the secondconnection state than in the first connection state for a same rotationspeed of the motor, the method comprising the steps of: switching theconnection state of the coils from the first connection state to thesecond connection state, and switching the bus voltage generated by theconverter from a first bus voltage V1 to a second bus voltage V2 higherthan the first bus voltage V1 in a case where the connection state ofthe coils is switched from the first connection state to the secondconnection state.